Complete Guide to Using the Correct Charger or Power Adapter (and What Happens If You Don’t)

Wait! Just because the plug for that universal adapter fits into your laptop or phone doesn’t mean it’s safe to use. Read this guide on finding the right charger or power adapter.

The other weekend, I sat down and sorted through all my random electronics junk. As part of that process, I took all my power supplies and adapters and threw them into a box. It ended up being a pretty big box. I’m willing to bet that any given household has a dozen or more different types of cell phone chargers, AC/DC adapters, power bricks, power cables, and charger plugs.

what happens if you use the wrong power adapter?

Having so many chargers can be pretty frustrating. It’s easy to get them separated from the phone or laptop or tablet, or router. And once that happens, it can be complicated to figure out which goes with which. The default solution is to try random plugs until you find one that fits into your device. However, this is a big gamble. If you grab an incompatible power adapter, your best case scenario is that it works, albeit not the way the manufacturer intended. The second worst-case scenario is that you fry the gadget you are trying to power up. The worst-case scenario is that you burn down your house.

In this article, I’m going to walk you through the process of digging through your junk drawer and finding the right power adapter for your device. Then, I’ll tell you why it’s so important to do so.

In a nutshell:

  • The following will cause damage to your device:
    • Reverse polarity
    • Higher voltage adapter than device rating
  • The following will cause harm to your power cord or adapter:
    • Reverse polarity
    • Lower current adapter than device rating
  • The following might not cause damage, but the device will not work properly:
    • Lower voltage adapter than device rating
    • Higher current adapter than device rating

A Very Brief Introduction to Electrical Terminology

Each AC/DC power adapter is specifically designed to accept a certain AC input (usually the standard output from a 120 V AC outlet in your home) and convert it to a particular DC output. Likewise, each electronic device is specifically designed to accept a certain DC input. The key is to match the DC output of the adapter to the DC input of your device. Determining the outputs and inputs of your adapters and devices is the hard part.

Power adapters are a bit like canned food. Some manufacturers put a lot of information on the label. Others put just a few details. And if there is no information on the label, proceed with extreme caution.

The most important details for you and your delicate electronics are the voltage and the current. Voltage is measured in volts (V), and current is measured in amps (A).  (You’ve probably also heard about resistance (Ω), but this doesn’t usually show up on power adapters.)

dc power connectors - round

To understand what these three terms mean, it helps to think of electricity as water flowing through a pipe. In this analogy, the voltage would be the water pressure. Current, as the term implies, refers to the flow rate. And resistance relates to the size of the pipe. Tweaking any of these three variables increases or decreases the amount of electrical power sent to your device. It’s important because too little power means your device won’t charge or operate correctly. Too much power generates excess heat, which is the bane of sensitive electronics.

The other important term to know is polarity. There is a positive pole (+) and a negative pole (-). For an adapter to work, the positive plug must mate with a negative receptacle or vice versa. By nature, direct current is a one-way street, and things won’t work if you try to go up the downspout.

If you multiply the voltage by the current, you get the wattage. But the number of watts alone won’t tell you if the adapter is right for your device.

Reading an AC/DC Adapter Label

dc adapter label

If the manufacturer was smart enough (or compelled by law) to include the DC output on the label, you are in luck. Look at the “brick” part of the adapter for the word OUTPUT. Here, you’ll see the volts followed by the direct current symbol and then the current.

The DC symbol looks like this: image

To check the polarity, look for a + or – sign next to the voltage. Or, look for a diagram showing the polarity. It will usually consist of three circles, with a plus or minus on either side and a solid circle or C in the middle. If the + sign is on the right, then the adapter has positive polarity:

dc center positive polarity

If there is a – sign on the right, then it has negative polarity:

dc center negative polarity

Next, you want to look at your device for the DC input. You’ll usually see at least the voltage near the DC plug receptacle. But you also want to make sure the current matches, too.

You might find both the voltage and the current elsewhere on the device, on the bottom or inside a battery compartment cover, or in the manual. Again, look for the polarity by either noting a + or – symbol or the polarity diagram.

Remember: the input of the device should be the same as the output of the adapter. This includes polarity. If the device has a DC input of +12V / 5.4A, get an adapter with a DC output of +12V / 5.4A. If you have a universal adapter, make sure it has the proper current rating and choose the correct voltage and polarity.

Fudging It: What Happens if You Use the Wrong Adapter?

computer on fireIdeally, you’ll have the same voltage, current, and polarity on your adapter and device.

But what if you accidentally (or purposefully) use the wrong adapter? In some cases, the plug won’t fit. But there are many instances where an incompatible power adapter will plug into your device. Here’s what you can expect in each scenario:

  • The wrong polarity – If you reverse the polarity, a few things can happen. If you’re lucky, nothing will happen, and no damage will occur. If you are unlucky, your device will be damaged. There’s a middle ground, too. Some laptops and other devices include polarity protection, which is essentially a fuse that burns out if you use the wrong polarity. If this happens, you might hear a pop and see smoke. But the device may still work on battery power. However, your DC input will be toast. To fix this, either replace the polarity protection fuse or get it serviced. The good news is that the main circuitry wasn’t fried.
  • Voltage too low – If the voltage on an adapter is lower than the device, but the current is the same, then the device may work, albeit erratically. If we think back to our analogy of voltage being water pressure, it would mean that the  device has “low blood pressure.”  The effect of low voltage depends on the complexity of the device. A speaker, for example, might be okay, but it won’t get as loud. More sophisticated devices will falter and may even shut themselves off when they detect an under-voltage condition. Usually, an under-voltage condition won’t cause damage or shorten the life of your device.
  • Voltage too high – If the adapter has a higher voltage, but the current is the same, then the device will likely shut itself off when it detects an overvoltage. If it doesn’t, it may run hotter than normal, which can shorten the device’s life or cause immediate damage.
  • Current too high – If the adapter has the correct voltage, but the current is greater than what the device input requires, you shouldn’t see any problems. For example, if you have a laptop that calls for a 19V / 5A DC input, but you use a 19V / 8A DC adapter, your laptop will still get the 19V voltage it requires, but it will only draw 5A of current. As far as current goes, the device calls the shots, and the adapter will have to do less work.
  • Current too Low – If the adapter has the correct voltage, but the adapter’s rated current is lower than what the device input, then a few things might happen. The device could power on and draw more current from the adapter than it’s designed for. This could cause the adapter to overheat or fail. Or, the device may power on, but the adapter may not be able to keep up, causing the voltage to drop (see voltage too low above). For laptops running on undercurrent adapters, you might see the battery charge, but the laptop is not powering on, or it may run on power, but the battery won’t charge. Bottom line: it’s a bad idea to use a lower current rating adapter since it could cause excess heat.

You would expect to see all of the above based on a simple understanding of polarity, voltage, and current. What these outlooks don’t take into account is the various protections and versatility of adapters and devices. Manufacturers may also build a bit of a cushion into their ratings. For example, your laptop may be rated for an 8A draw, but in reality, it only draws around 5A. Conversely, an adapter may be rated at 5A, but can withstand currents up to 8A. Also, some adapters and devices will have voltage and current switching or detecting features that will adjust the output/draw depending on what’s needed. And, as mentioned above, many devices will automatically shut down before it causes damage.

That being said, I don’t recommend fudging the margin under the assumption that you can do the equivalent of driving 5 MPH over the speed limit with your electronic devices. The margin is there for a reason, and the more complicated the device, the more potential for something to go wrong.

Have any cautionary tales about using the wrong AC/DC adapter? Warn us in the comments!


P.S. Wall adapters that give you a USB port for charging aren’t nearly as tricky. Standard USB devices have a 5 V dc voltage and a current up to .5 A or 500 mA for charging only. This is what allows them to play nice with the USB ports on your computer. Most USB wall adapters will be 5 V adapters and have a current rating well over .5 A. The iPhone USB wall adapter I’m holding in my hand right now is 5 V / 1 A. You also don’t have to worry about polarity with USB. A USB plug is a USB plug, and all you usually have to worry about is a form factor (e.g., micro, mini, or standard). Furthermore, USB devices are smart enough to shut things down if something isn’t right. Hence, the oft-encountered “Charging is not supported with this accessory” message.

Feature image by Qurren – GFDL ( or CC-BY-SA-3.0 (, via Wikimedia Commons



  1. awraynor

    I always used the “if it fits it’s the right one mentality”, guess
    that wasn’t such a good idea.

    • Steve Krause

      Yeah…. well I always paid attention to the voltage however I never knew about the polarity. Great tip Jack!

    • Jack Busch

      I learned that lesson early, when I plugged in my tiny tiny cassette player into this mammoth brick. I got my first whiff of blue smoke and I could no longer listen to my tapes to practice for drum lessons. I ended up flunking drum lessons, but for different reasons (lack of talent).

      • Kathi

        Jack, I appreciate this article and I feel fairly confident I can go ahead and buy this power adapter I found on Amazon, but still, I’d like your opinion if I may.

        The back and side of the radio clearly say, Power Source: 7.5V 400mA AC/DC Adapter
        The little drawing shows the + sign on the right.

        The power adapter I am about to buy says, 7.5V 2A for 400mA 500mA 800mA 1000mA DC Adapter Power Supply 5.5mm2.1mm/2.5mm

        What’s making me question myself is that “2A” which is not on my radio.

        Thoughts? (And thanks so much.)

        • Not Jack

          The 2A is referring to the max current of 2Amp the device can handle. The article stated that an adapter with a current too high won’t cause damage to the cord or device. Since the radio requires 400mA (0.4A) it should be perfectly safe to use for the radio as the adapter says so itself at the stated “400mA” on the label.
          This comment section doesn’t have dates on it so I hope this message reaches you before several years have passed.
          My name isn’t Jack but I hope I could help.

          • Steve

            THank you so much! Makes sense.

          • pit

            Since when?

            “the device will not work properly’
            IF “Higher current adapter than device rating”

            If that was true 99.9% of your devices you use at home would go bang.

            One can connect a P.S. that can deliver 10000000A to any device whose voltage rating is the same as the P.S’s. (more or less depends on the device)

            V should be same (more or less-depends on the device)
            A (of P.S.) same or higher

      • Anjali

        Jack of Talent, thank you very much. You may have just extended the life of my Hoover stick vacuum (the charger is no longer available).

    • Murray

      Way too complicated tech-speak, and yes, nearly impossible to read the specs on the adapters. The whole power adapter electrics situation is a global miserable nightmare with nothing I’ve seen resembling a nice easy color code or similar to make it simple and uncomplicated. All I can do is use something that fits, and if the adapter dies or the appliance dies, then it all just goes in the rubbish bin. That’s with what I own now. For future purchases I might try and get multiple adapters when the appliance purchase is first made.

      I’m going to try these “universal” adapters and see if that works. If I could get one style of adapter that worked on every computer appliance/device (including external hard drives) then I’d be willing to pay a mint for it, and then get multiples of the adapter for backup.

      • tami morrow

        i couldnt agree more isnt there a simple chart i can input the info of the ac or dc adapter and it will give me the crossreference electrical info on the side … EXAMPLE my adapter reads input output exc. on the right u see the same info for the compatible charger exc .. for the product u r trying to either power p or turn on .. and not in a list for like computer dvd layer hone exc but in the INPUT OUTPUT \compatabiity for. its that simple if someone understands the math then please do the problem and share it w those of us who just dont

        • R Morrow

          The chart you are both looking for is already (usually) included in the wall adapter and on the appliance. If your appliance says input: DC 12v/1A, get an adapter that says Output: 12v/1A DC. All you do is find a wall adapter with an output that matches the input of your device. There are so many different wall adapters that a list of them all would be impossible to maintain. Every new device that comes out usually has a custom one.

          I wasn’t aware of the polarity issue he brought up, but I will take that into account from now on.

          • DARRELL MAK

            Article has a contradiction. It first says a device will not work properly if you have a “Higher current adapter than device rating.”

            But later, it says, “If the adapter has the correct voltage, but the current is greater than what the device input requires, then you shouldn’t see any problems.”

            I’m guessing the latter is correct.

      • Jim

        You must have deep pockets. It’s not that complicated. This is good easy to understand information and right on the money.

      • s c

        keep your head up Murray! Reread the article and try to follow the examples, check other websites as well – if you really want to understand this – it just takes time and maybe even somebody in person to show you – if you happen to know somebody that is good with this stuff in your neighborhood or your family

        Once you understand the terms he’s explaining- the three variables (voltage, current, polarity)- and where to find them on your device and your power supply, you’ll be golden.

        It just takes time and frustrating failure to finally identify what you’re looking for, you got it

        • Pauz

          Well said. – – -Fun articular to read.
          Learning a new skill takes time and practice.
          Often a good bright light and finding the right angle to read the lettering and symbols. A good magnifying glass is a necessity for me!

          Sometimes the information is printed on a label that is worn & torn.
          Then, I will get the information with a multi-meter mapped-out the the wires and the plug. I never had to measured the the size of the connector’s post, (on the male end), but I’m glad this artificial brought up the issue. Manufacturers follow a set industry standard thanks to the IISE
          Institute of Industrial and Systems Engineers
 home website
          The world’s largest professional society dedicated solely to the support of the industrial and systems engineering profession and individuals involved with improving quality and productivity.

      • Not Jack

        The short version: Voltage (V) should always be the same for both adapter and device.
        Polarity (plus on the left side or plus on the right side) should always be the same for both adapter and device.
        Current (A or mA) of the adapter should not be lower than the current of the device but may be higher.

        • Meg

          This was the best simple summary of the article I could have imagined. I turned it in to a note on my phone to remember forever.

          Voltage: adapter = device
          Polarity: adapter == device
          Current: adapter >=device

          • Talaat

            I am using adapter 15 V – 0.5 Am- 7.5 W
            Instead of the original adapter 15 V- 0.36 Am-5.4W
            For my shaving Mashien
            Is ther any damage can happen to my shaver

      • Veronica

        I have a zillion power supplies too and I don’t know what to do with them.

        Trying to figure out what 15 VDC and 100 mega amps means


      all of these devices should have a label of the maker and product it came with. But that would prevent us from being forced to buy more crap!

      • Not Jack

        And that’s why I have a label maker. It’s the first thing I do when I buy a new gadget.

      • Talaat

        if using adaper 15V,0.5Am,7.5W instead of the original adapter 15V,0.36Am,5.4W is it wrong

        • pit

          Nothing wrong.The adapter will be cooler when working – that’s good.

    • ken

      I have a small motor vibrating motor for a table . its a 12volt DC 100ma.
      does that mean i should look for a plug that is 12dc with .1amp. If so can i get a plug that can be 12 volts DC 5 amp i’m thinking if i’m at 100ma which is smaller then max 5 amp i should be ok

    • Garry

      I can’t see how to set up a new comment. So to correct something in this information

      ‘If there is a – sign on the right, then it has negative polarity:’.
      This is not correct. This relates to the centre and the outer of output connector. The image is in fact displayed in the reverse view to this on some adaptors. So not left of or right but whether the line goes to the centre(dot) or the outer(C) is the way to read it. So if it were the reverse image it would in fact be left and not right!!!!

      • Jonathan

        I noticed the same thing – I was a bit thrown off at how an explaination for people unfamiliar with electronics, contained an “assumed standard”. The only standards that electronics (usually) conform to are in regards to the wire gauge and respective maximum current. Despite many different international standards, most of these devices are made in China with dangerous variations of quality control and even a manufacturer’s design engineering. A multimeter is very inexpensive and can confirm a lot of infomation that otherwise is entrusted to be accurate from potentially low QC factories.

  2. Brian Burgess

    I have always been pretty anal about making sure the voltage, mA and all that. Many times struggling to read what’s printed on those plugs. Get’s very annoying.

    On another note, nothing is more irritating than the plugs that are proprietary — the old Apple 30 pin ones for example.

    Also, I usually put a sticker on my plugs and label them so when I do go in to the junk drawer I can find what I need easier.

    • Jack Busch

      Good tip. Haha yeah I forgot to mention I also had a box of “Old Apple stuff.” Between my wife and I, we have quite the graveyard of proprietary Apple pluggers.

    • Steve Krause

      Yeah, I forgot to mention I started labeling new power adapters about a year ago so I know what they go to. It’s helps but it’s not a perfect system. Hard to read black sharpe on black adapters… ;)

      • Barbara

        I put nail polish dots on my cables AND the devise. I can match color and design.

      • stalino

        Uh, they have SILVER ink SHARPIES that look legibly awesome on black and you can forget about printing labels.

        • Steve Krause

          So you’re saying I need to plan better…. hehehe you are 100% correct. Great tip! Have you found it doesn’t rub off either over time? Obviously the label I put on a few lasted as long as it took one of my kids to see it…

          • stalino

            Hehe, at age 80+, I’ll probably rub off or out before the silver Sharpie ink does. Be careful and gentle with your plugs like you are with your wimmin and they will do you fine through the years.

      • Fredx


      • Steve Davis

        I’ve found that ‘P-Touch’ labels come in very handy for this type of application. I made the decision to use the p-touch after frying a brand new phone system – polarity issue. Polarity is a big deal – labeling – a big help!

      • Alice

        I make a label on my DYMO label maker and wrap it around the cord for each device

      • Mary Anne

        paint markers that are colored work on many black things including socks

      • Richard Nelson

        A silver sharpie works very well.

    • Dwight Foster

      This makes more sense than all the electronic matchmaking. It’s my opinion that manufacturerers should do the labeling; place a device label on the adapter brick for problematic adapter matching.

  3. Elaine

    You don’t mention watts in the mix. My old adapter was 19.5V, 3.34A, 65W. The universal adapters are 90W. I was leery of their claims that it would be okay, since they want to sell me a new laptop after I fry it. I ended up getting an used replacement from an independent computer repair shop for $20. Even the manufacturer, over the phone, wanted $65 for a new one and 10 days shipping!

    • Bob

      Watts (W) is the product of Volts (V) and Amps (A). In your case, 19.5V x 3.34A = 65.13W, which is about the 65W listed. The universal power supply has circuitry to adjust the voltage to the needed level and the maximum current would also change such that the product is 90W. That adapter would have been fine. As the article states, you do want to match voltages between the power supply and device, but you can us a power supply with more amps than needed. The device will only draw as much current (Amps) as it needs at the time.

    • Cory wichman

      Yep, Bob’s right.. and also he did briefly mention Watts.

  4. Caitriona

    If a step up/step down converter was used on a US appliance in the UK (110 –> 220V) and it was plugged in the wrong way, with the 220V continuing into the appliance, which promptly stopped, is there any fixing the appliance now?? Thanks!

    • Andy Russell


  5. Denz

    These tips are very valuable. I got a lot of ideas that are very helpful in dealing with my power adapter problems. please do keep the good work rolling.

  6. Sean

    I don’t know that she will ever come back to read this, but for the benefit of future readers, I thought I’d respond to Elaine’s comment, above, where she says, “You don’t mention watts in the mix.” In fact, the author did, but only briefly. (Excellent article, btw – I tip my hat to you, Mr. Busch. :-) )

    The article mentions, “If you multiply the voltage by the current, you get the wattage.”
    Also, under the “current too high” section above, it explains that it’s OK if your power supply is rated for MORE current (amps) than the device needs; the device will only draw the current it actually needs. But it’s not good to use a supply rated for less current.

    Imagine you want to tow a speedboat. Normally, you would hitch the trailer up behind your car. Imagine, instead, you hitch the trailer to the tractor of an 18-wheeler tractor-trailer. What happens? Not much. The tractor pulls the boat effortlessly to wherever you want to go, and most of its power is never used. Now imagine you hitch the boat trailer to your bicycle. What happens? You may not move at all, or you may be able to move the boat, but you are going to overheat and possibly die in short order. Same deal. Extra amps are fine, just not used, like the tractor. But with insufficient amps, your device may not work at all, or it it does, it will be hard on the power supply, which may overheat and/or fail – like the bicyclist trying to tow a boat. Not enough power.

    Those two concepts combine to answer your question; let me explain with an example.

    Suppose you have a laptop that came with a 20 volt power supply, with an output of 3.5 Amps.
    You go to the store for a replacement supply, and they have two kinds of 20 volt power supplies, a 65 Watt and a 90 Watt. (Which is actually the case at my local computer shop, NCIX, except they’re 19 volts. But 20 makes for simpler math.) Which one should you choose?

    The original power supply put out 20 volts at 3.5 amps; 20 x 3.5 = 70 Watts. So your original power supply could produce up to 70 watts of power. You could buy the 65 watt adapter and *probably* be fine – it produces nearly as much power as the original, and your device probably doesn’t draw its maximum current most of the time. However, I’d go with the 90 Watt supply, since it is more power than the original could possibly supply; kinda like switching from your normal boat-towing car to a pickup truck.

    To complete the example, suppose they also offered a 200 watt power supply. (I don’t know if such things exist, but feel an urge for completeness in my story.) That would be like towing your boat behind a locomotive – it won’t hurt anything, but you’re wasting money buying an excessive amount of power that you will never use. If the manufacturer gave you a 70 watt power supply with your device, you can safely assume that device shouldn’t need more power than that.

    It’s already covered in the article, but to reiterate: excess AMPS are OK, excess VOLTS are NOT. If you have a device that needs 20 volts, and you feed it 100, your device will probably not survive the experience, though may entertain you with some fireworks for a few seconds.

    • Enea Antonicelli

      I have to leave a reply and say that it is a breath of fresh air when educators such as yourself and the author of this article bless others like myself with perfectly concise and easy to understand knowledge. Thank you so much for explaining this so damn well.

    • Enea Antonicelli

      I forgot to ask and it’s worth a shot since I rarely come across people like you; Would you happen to have a similarly beautiful explanation for how resistors work in series and in parallel? I am having trouble understanding how to determine the quantity and raitings of Aluminum Clad resistors I would need in order to bring a 12×12 1/8″ aluminum plate up to a temperature of around 100-120 C. Also how to wire them. They are often labeled as such: (50W 1.5 ohm J).. Explanations I get on this are often confusing for me most likely because I am having trouble grasping the basic concept of parallel resistors and “power” output along with the labeled ratings.. Maybe an analogy might do the trick I just can’t seem to find a good one. Thank you kindly in advance and no worries if you can’t.

      • Mike

        Series = R1 + R2 + R3
        Parallel = 1/R1 + 1/R2 + 1/R3

        Think in terms of speakers, hook two 4 ohms speakers in series and the total R will be 8 ohms. Hook them up in parallel and R will be 2 ohms.

        R = V/I
        V = I*R
        P = V*I
        I = P/V
        V = sqrt(P*R)
        I = sqrt(P/R)

        so…in your example:
        P = 50 watts
        R = 1.5 ohms
        I = 5.8 amps
        V = 8.7 volts

        • John KaBang

          To calculate the value of parallel resistors:
          If there are only two resistors you can use: Rp=(R1*R2)/(R1+R2)
          If there are three or more resistors then use: Rp=1/((1/R1)+(1/R2)+(1/R3))

    • Kelly

      Great stories, great analogies, but it would have been soooo much better had you given Elaine an answer to her question!

      • Francesco

        Hi Kelly. I believe Sean did respond to her question. Elaine just needs to be sure that the Voltage and polarity on her universal adapter matches that of her device and she will be fine. Once she knows if the Voltage matches then she can buy a power adapter with a higher Wattage without worrying about damaging the device (but not a lower Wattage).

        The amperage (current) of the plug can be higher than that of the device but not lower.

        SO in a nutshell, Voltage and polarity must be the same. Current must be same or higher. Wattage can be higher than original as long as the voltage is the same After you know the voltage it is simple to calculate the Wattage… If I may quote the author of this article: If you multiply the voltage by the current, you get the wattage.

        Hope this helps and that I didn’t confuse the matter. I am new to this and am not an expert like Sean or the author (great job guys).
        God bless

    • MikeM

      If I am following this thread correctly…
      my “old” AC Adapter specs:
      -AC Input: 100 ~ 240V 50 ~ 60Hz
      -DC Output: 19V 12.2A 230W

      which the math equals 231.8W

      Another “replacement” unit specs:
      -AC Input: 100 ~ 240V 50 ~ 60Hz
      -DC Output: 19.5V 11.8A 230W

      which the math equals 230.1W

      Is the “replacement” unit compatible and safe to use as my replacement AC Adapter for a HP touchsmart All-in-one PC?


      • EmilN

        “-DC Output: 19V 12.2A 230W
        -DC Output: 19.5V 11.8A 230W

        – Yes, they are likely interchangeable even though voltage is not the same.
        This is because the voltage difference is within specs, and I am GUESSING you could go even higher or lower in voltage.

        Those are some very beefy supplies by the way!

    • YK

      Sean, I like your explanation. Well fit the mind for a layman like me. Thank you!

  7. dan

    I used the reverse ac adapters for the base and handset of a uniden phone (D1788) which I didn’t realize since it worked fine for 8 months, the difference in output was 7.8V vs 8 V. Now the base unit won’t power on….any idea whether this can be repaired with relative ease or if I’m S.O.L.?

  8. viraj

    my power bank is having 5.1V output and my phones’ charge battery is 4.2 V
    will it harm my battery? if yes than how much??
    thanks in advance.

    • Muhd Danial

      No, it don’t cause any harm to your battery. The 4.2V is just the voltage that your battery will power your phone. The standard volts to charge your battery is 5V, (It depends on the manufacturer that make your phone). The safe way, you need to check your original phone’s charger plug and find the voltage ‘V’ symbol. If it’s stated 5V, you are not in trouble , because you can use the USB cable to charge your phone by the powerbank’s port. The USB also is the symbolized for 5V voltage. So, you don’t have any problem to connect your phone to your computer or powerbank. Your phone also will receive a 5V voltage and will damage if above that rating. But, a Samsung product, The Galaxy Note 3, received a 5.3V and 2A of electricity, which received 10.6W (watt) of power. You also need to calculate the power ‘W’ (wattage) of your phone’s charger plug and compare it with your powerbank, power ‘W’.
      For example, the Samsung Galaxy Note 3’s power is 10.6W (5.3V×2A) and a powerbank of two port which the output is the same but the current is different. The output one is 5V/1A and the other one is 5V/2.1A.
      Let’s calculate the power of each output :
      Output 1 = (5V×1A)
      = 5W
      Output 2 = (5V×2.1A)
      = 10.5W
      So, you can see the power of the Samsung Galaxy Note 3 is 10.6W and the powerbank is 5W and 10.5 W. You can choose which port did you want to connect the Samsung Galaxy Note 3 to the powerbank. The 5W of the output 1 is less and the phone will take some time to full up the battery. But in the port 2 you have more power and a less time you need to full up the battery. Now, you can calculate your phone charger’s power and compare it with your powerbank’s power. Alright, I hope this message will help you with your problem. Thanks.

  9. Anne

    Hi Jack,
    The other day I accidentally threw away my husbands beard trimmer charger. So I made a mad dash to Radio Shack to replace it. It requires a 4.2v and 600 mA charger. They only had a 4.5v 700 mA charger and he tried plugging it in but it didn’t work…I’m afraid it’s fried because we can’t turn it on anymore. Any ideas???

  10. Charlie Montague

    I lost my PS2 Super-Slim power cable, and I want to play the PS2, but I have one for my PS3.

    My PS3 power cable fits in to the PS2 fuse box, but has a negative polarity, whereas the PS2 fuse box (AC Adaptor) has a positive polarity.

    Furthermore, on the fuse box, it says on a label on it: “INPUT 100 -240V ~ 1.5A”, and the PS3 power cable says “250V 2.5A”.

    I’m not sure whether I should use the power cable for the PS2, or try to buy a PS2 one.. .

    • James

      It is important to know that this is AC power not DC. The PS2 power supply turns the AC voltage in your wall from the power company into DC. The rating on the power cord is just a max voltage rating because in other countries they may have power rated at 250V. That is why the PS2 power supply says 100- 240V because it can turn AC power between those voltages into the power appropriate for the PS2. So long story short if it fits it will work just fine.

  11. Raul G

    I’m using an adapter for my laptop which has the right polarity but the voltage and current are not the same. The original has: INPUT: AC100-240V-,50-60Hz, 1.5A. OUTPUT:19V. 3.42A. Now I’m using: INPUT: 100-240 1.7A 50-60HZ. OUTPUT: 20V. 3.25A. I’ll be glad if you can tell me if this is totally wrong for my equipment or if I could reliance in my adapter. Thanks in advance ;)

  12. barrystyle

    Using a higher current charger (than the laptop is rated for) will not cause damage to the laptop; as stated earlier.

    The device will only draw what it requires from the power pack. The power pack isn’t ‘forcing’ the current down the neck of the laptop.

    A better way to think of this would be in terms of a desktop computer. While a motherboard may only call for a paltry 50W (in combined 3.3v, 5v and 12v rails); you would be more than safe to use a 1500W high performance power supply – as only 50W will be drawn from the powersupply itself.

    Feel free to give it a go.

  13. Jeffery

    Hello, i would like to ask what will happen to my laptop if i replace my original 19V and 3.74A adapter with a 19.5V and 3.6A adapter?

    Will a 0.5V higher damage my laptop? Thank you very much

  14. Sue

    My problem is a little different. I know I have the right two pieces they came together and I’m trying to charge up my tablet, The two pieces do not fit together flush, there is a gap. I’ve had it plugged in for over eight hours and it still does not act like it’s completely charged. I had the same problem with my Kindle once I changed it to a different adapter that fit flush it charged up in no time, it certainly did not take eight hours or more. Am I experiencing the same type of problem I had with my Kindle? That it must have come with a faulty adapter?

  15. Bob

    just a tip that has worked to somewhat solve the above problem for me:

    when you buy any device that comes with a power adapter, take a black sharpie marker and write on the top of the adaptor what device it is for. Just wish I had always done this (guilty of still having a box of adapters that are unmarked)

    • stalino

      If the device is black, as most are….. then as I mentioned previously, Sharpie has SILVER ink marker that will stand out against the black device. It also is re-markable (pun intended) how it stands out against a host of other color backgrounds including white eggshells to mark the old from the newer ones.

  16. Forrest

    Hey so im having a bit of trouble here.. not so good with this stuff, Anyways my device a numark total control mixer has a plug in the back that says, POWER DC IN 6V 1A and my question is can i use any of these adapters?

    Device: 6V 1A

    Adapter1: Output: 12VDC 500mA

    Adapter2: 15V 1.5A

    Adapter3: Output 7.5VAC 350ma

    :S any advice would be great thanks.

    • John

      No, it is too high a voltage (12v versus the 6v you need!)

  17. dawn

    You may have already answered my question but…..if you use the incorrect charger on a much larger heavier device, can the charger be sort of reverse loaded up with electricity from that actual battery pack and then when used on the correct very delicate device that power fries the sensitive devise? I believe this is what happened to me. The bigger device has a very heavy battery pack like a couple pound battery and the device the charger was made for is super small and delicate.

  18. ram

    today i tried to connect my 5v dc (USB power) sound with 12v dc adapter after that it shows power on bu no sound. i dont know exatly what happened ro the device?

  19. Tim K

    HI. One small issue with your article …

    Under the Polarity Section you said: “If there is a – sign on the right, then it has negative polarity:”

    This is not necessarily true. It really depends which way the “C” is facing. I am looking at an adapter right now that is POSITIVE but the “-” sign is on the right, and the “+” on the left. However the C is backwards facing the “+”. (And no, I don’t have it upside down.)

    Same can be true for the reverse of course … it all depends on which way the C is facing.


    • Some Bro

      Thanks for confirming this! I came here looking for info about this scenario.

  20. Al C

    The adapter wires are solid black and the other is black with white strip. Which is the positive?

    • Carpenter940

      Positive is the one with the stripe

  21. daemon

    excellent article.

  22. Steven

    Hey, I plugged a AC 5.5v 2.5A power adapter into a DC 5V charged device, and now its not working, did I do something bad to it?

  23. Martin

    Brilliant article, which I too read too late to save an effects pedal for my guitar.

    On the polarity though, If I have an adaptor rated the same as my machine, but the polarity is opposite, can I not just cut the wires, switch them over and …. why woouldn’t that work?

    • Carpenter940

      It would work… I’ve done that many times.

  24. G J BUNTON

    I own a few 18v and 24v cordless drills which are perfect except for the battery which costs almost as much as the drill brand new.
    I want to use a transformer to connect my 24 volt drill to 240 volt mains.
    The battery is a 1200mAh Ni-cad.
    I have a laptop charger that puts out 19.5 volts/4.7 amps can I run the 18v drill using this?
    Thank you

  25. Nima

    Hi People,

    Could anybody please dumb it down for me without too much details if I could use an AC adapter with Input : 100—240V ~1.5A (not 2.5A) 50—60Hz as a replacement for my original AC adapter which was an Input : 100—240V ~2.5A 50—60Hz?

    Muchly appreciated.

    • James

      You need to look at the OUTPUT the input does not matter as long as it was bought in the same country. Even then it does not matter the input is just an acceptable range. For example if you bought a power supply from Europe that says INPUT: 240V ~1.5A 50hz then it will not work in america or japan or several other countries. The range you are talking about will work in any country. It all depends on the OUTPUT of your devices.

  26. mote

    That was certainly great and very interesting and brilliantly informative, thank you so much.

  27. Matrix

    I had Fujitsu Ah531 series laptop that uses 20v 3.25a output. Today I bought a 19v 4.22a charger, initially it was working fine till it recharged about 35% of battery and suddenly stopped working, now its not charging anymore. The charger was hot when I disconnected it. I am nervous whether it has done anything harmful to my laptop….!

  28. Corwin

    So my adapter matches the Voltage and current but not the polarity so i gues i should not use this adapter. the input polarity is + c – the adapter output is – c + but the fitting fit perfect but I’m not going to plug it in until i get a response

    • Some Bro

      Don’t do it! You’ll ruin it.

    • EmilN

      With a little skill, you could swap the wires around.
      Plus then becomes minus, and vice versa.

      Just make sure you did your polarity test correct in the first place.

      • Carpenter940

        I second EmilN’s comment

  29. cindy

    I have an emergency flashlight but I do NOT have the adapter to charge the sealed lead rechargeable battery, it is old and is some unknown brand. I found one on ebay and the seller sent me picture of the adapter. It doesn’t have the little circles diagram, but it does have a drawing of the tip (male) with a ‘+’ near the end of the tip (the smaller part of the “male”) and a “-” near the top with the wire. The flashlight has what I would call the female, a tube to plug the tip of the adapter into.I bought a velleman switching power adapter which I have to set the center polarity to either plus or minus. Do I want center positive?I am setting my adapter output on 9V (this is to charge the flashlight battery). Here is the info I have on the adapter and battery: Class 2 power supply Input 120VAC 60Hz 21.6W Output 9VDC 500mA. Adapter plug looks like a stereo headphone jack and I don’t know which part is negative/positive. Battery specs: 6V 4.5A. I have a photo of the adapter if needed. Thanks!

  30. Akit

    Hi this might probably be reaching you late but the receptacle “female” has a positive center and a negative surrounding while the “male” will have some gaps along it’s metal shaft. The tip is positive the usually plastic gap separates it from the next segment which is negative. This applies to most if not all of such design including the headphones and them huge speakers.

  31. Rhyknowscerious

    Spectacular job on this post. Very helpful. I’ll recommend this page to everybody I know. Great job !!!

  32. Chuck

    Great article. I’m just curious about something:

    Should I be careful of the fuse in the plug I’m connecting the adapter. My input states 100-240v 1.2A – does this mean I should be using a 1A fuse in my plugsocket? Most plug is fused at 5A as standard – could this damage my adapter?

    Thank you for any help.

  33. Julia

    So, it is as simple as finding an adapter with the same voltage and polarity as the device you need to power?

    or am I missing something? Kind of feel that I am, hence the question.

    Also, if these details are missing from either the device or adapter is there a way to test them and find out what the voltage and/or polarity are? Perhaps using a voltage meter?

  34. Mike

    What happens if I am powering lights that require 1250 mA for 2 lights and I power 4 of them with 1000 mA. They seem to be almost as bright but will it overheat the adapter, burn it out or just run the lights the best it can with the mA it has?

  35. Akit

    @ Julia, yep its that simple and if you’re in a situation where you need to test power output, grab yourself a meter. digital ones are least confusing. Bear in mind DC devices are polarity sensitive and be sure you know how to use a meter less you fry it. Cheers…

  36. Keith

    Well I have been doing some searching for batteries for my Asus A551XM Laptop. In the videos/blogs that I have seen it shows the battery number as A31N319 and it is rated at 11.25 volts, yet I can see on the power adapter supplied with my laptop that it is rated at 19 Volts output, so, my question is, wouldn’t this cause an issue with the battery receiving 8 volts too much???

    • Matt

      No, the laptop gets 19v, but then reduces the voltage to output to the battery. Also, charging voltages are greater than rating voltage. Its like filling a balloon. You can’t inflate a balloon unless you put higher pressure into it.

  37. Matt

    Back before I knew alot about electronics, I plugged a 16V adapter into a device that needed around 7 volt. It turned on the first time. I turned it off, it made a little different noise the second time and then it didn’t work and I smelled smoke.

  38. Rajesh

    I have a Creative SBS 370 which uses and AC Adaptor of rating 11.5V 1600mA . It stopped working . I was not able to find an AC Adaptor in any shop with such a rating and it was the same condition with online sites too.I read in a forum that 12 V 1.5A DC ADAPTOR also works with it!!!!!


    But i did decide to give it a try because when i opened the plastic box of the Creative AC Adaptor, i found that it had only a stepdown transformer inside and i concluded that the AC TO DC Converter circuit had to be located inside the Woofer box to which the AC 11.5V 1600mA was to be fed.
    So, instead of the AC 11.5V 1600mA , I was giving 12 V 1.5A DC to the WOOFER.

    The Speaker simply started giving the audio. But i found that the output of the woofer was like around 90% to my satisfaction than when it was working on the original Creative Adaptor.Besides the Adaptor is getting heated up. A movie is like for 2 to 3 hours Max and it works without any problems . One more thing which i found out was that the adaptor was getting heated up even when the speaker was not switched ON.

    It has been a week now and the speakers are still working.

    An i am still confused with the AC DC FLOW .

    • James

      The adapters are just really similar It may never cause a problem then again the speaker or the adapter may give out. 15A vs 1600mA is 0.1A difference. 11.5 vs 12 is .5 v difference. 80w vs 80.4W is 0.4W difference. Power adapters numbers are just averages and never exact so I don’t recommend it but if its your only option and it works then you have no choice as long as you can live with the risk.

  39. Mike Stringer

    Is there a website to look up an adapter that you have no clue what device it is for?

    • Matt

      If you look up the part number on amazon, theres a good chance there will be a mention on what it is used for. Most of the time, companies will just buy an adapter from DVE or something for the specs they need (tip size, mah, voltage, polarity) and will work with a bunch of devices with the same needs.

  40. Gurdeep

    thanks for this informative guide . but i got stuck in a little different situation. i have bought a new laptop adapter which is of the same voltage , current and polarity. but this one gives me a little shock (just itching) sometimes when i touch any usb port or hdmi on my laptop .can you say what’s the reason for the same.

  41. Jay

    I need a 500mA 4v adapter and can only find replacement 500mA adapters that provide either 3v or 4.5v. It’s for a watch winder (not anything too elaborate or expensive). From your excellent example of a water hose, I can see that: if I ran it on 3v, it would simply turn slowly; if I ran it on 4.5v, it may burn up the motor. Is .5v enough to really be concerned if I chose to use the 4.5v setting? If it were a sensitive piece of electronics necessary for national security, I would feel differently.

  42. Matt

    I do have a few 4V power supplies in a box somewhere. I know they are 4V because I though it was a rather strange voltage. I could probably sell you one for about $10

  43. Jay

    Very reasonable. Please reach out at your convenience: jayaallen *

  44. rony

    if i use 19 volt 3.5 amp on my device ……the original adepter was 19 volt 8amp….what will happen??

    • Matt

      Probably not much. If it has a battery, it probably won’t charge, it might charge if the device is not running. Theres a good chance it won’t turn on, and even if it does turn on, it will probably shut off soon. The adapter will run hot until it can’t handle anymore and either turn off or melt.

  45. josh

    i have recently moved to Canada from australia and received a game console from australia i pluged the console in and it turned on completely normally but when i turned the tv on the image began to slowly flicker and scroll down the screen repetitively is this caused by the difference in voltage between the two countries or is it a fault with the console. if it is voltage problem will a converter fix it?

  46. Amy

    Get, easy to follow overview. Those Apple parts get tricky as the iPad cable and USB plug are 2A and the iPhone cable and plug are 1A. Helpful to know…if you label them when you get them..

  47. Gareth

    This is an excellent article; thank you.

    A concern I have is with finding REVIEWS for Chargers // Power Adapters// Universal Laptop Power Adapter// AC/DC adapters, in the hope that the buyer knows which is the best quality product: it’s not necessarily the most expensive, and the cheapest might also be good.

    Another concern is that a dedicated adapter provides stable, clean voltage and a universal does not. Perhaps a review will address this … if it existed!

  48. Kris

    I have a universal adapter that allows you to switch polarity. I’m trying to figure out the diagram of the polarity symbols. It must be an older adapter as I don’t see examples of these symbols anywhere on the Internet. My device is a negative polarity and need to know which polarity symbol on the adapter matches negative polarity. Can you help?

  49. Hami

    First of all like to appreciate for such nice and informative article. Need to ask one question. I have an internet switch device which originally has adapter with following specs: output 9 volts —500 miliamp. But this adapter stopped working (may be it was in use for 3 years). I replaced it with other adapter with following specs:output 5 volts —600 miliamp. My device is working fine so far. My question is should I continue to use this adapter for my device or i should go to market and look for a new adapter with specs like original one. Thanks

  50. Andy

    I have a US product with a US power adapter (110V AC to 5V 2A output). If im using it in Australia with a 240V to 110V step down transformer rated at 50W Max output power and 0.45A max current, will this cause any issues.

  51. Bill S

    When looking at the wires on the output side (dc) there are a pair of wires leading to the end plug, on some, one of the two (pair) has a solid white line on other models a dashed white line, what is the difference, my guess is that whether solid or dashed white line signifies + the positive lead? Anyone know for sure?

  52. MARLON


  53. joyce

    I thought the polarity was which one( + or -) had a line to the center of the circle, not right or left! good to know!

  54. MLK

    Quick question: Am I supposed to match the specs from the power adapter to my laptop battery or the laptop itself?

    OEM Specs:

    Battery: +10.8V 5200mAh, 56W
    Laptop: +19V 3.42A, 65W

    • Carpenter940

      Match to laptop. The laptop in turn handles the battery needs.

  55. Mike Fredrick

    I just bought an old 1960’s electronic piece that has two posts on the front for wiring it up with 6 volts. Can I just buy a 6v wall transformer and cut off the ‘plug’ and just use the bare wires for a connection? I know that I have to observe the proper polarity, but I can’t seem to find a transformer that is provide with just bare wires.

    • matt

      You would want to check how many amps the device requires. Also, you might want to check the adapter with a voltmeter. if its not regulated, it might be putting out way more than 6v (putting a load on the adapter drops the volts)

  56. opara wisdom

    hello please is it possible to use 20volts adapter on 19.5volts laptop

  57. Dave

    – – – – – – –

    so if this is all that is on the power adapter, is it center plus or center minus?

  58. Norm

    I have a question and I really don’t care if I sound dumb. My tablet power adapter wires broke. Bought a new charger and it appears the pin is wrong size. I was going to splice the two tother but the old charger had an out put of 12v 1.5a and the new one is 12v and 3a. Plus the gauge of the wire is different. Anyone here that can help it would be greatly appreciated.

  59. Chris Gerhartz

    This was really helpful thank you.

  60. doh

    THANK YOU for this article!!!! I accidentally-on-purpose used a 5V 2A adapter with a 12V 1A device and the device conked out on me. Your article gives me hope that, if I spend a few bucks at Radio Shack, I can revive my device by buying the right adapter. (I just assumed that, if the adapter fit the hole, it was compatible with the device. Doh!) Again, thanks.

    • matt

      I’m surprised that it ruined it. most likely nothing would have happened…unless the polarity was wrong. I have a lot of extra 12v adapters,if you know the tip size and polarity, I could send you one for about $10

      • doh

        Just saw this. Thanks for the offer. I went to Radio Shack and bought an adapter that can be used with multiple tips, along with the correct tip for my device, and all is well again.

        So, the wrong adapter did not actually ruin my device, but the “wrong” adapter itself is now dead. Go figure.

  61. Christine

    What does the m mean in 300mA for example?

    • Steve Krause

      Milliamperes. So 300mA = 300 milliamperes.

      • Christine

        Thanks! Some adapters just have a designation like 20W or 16W on the Input line, one has 300mA on the input line. What is the significance of that, if any?

      • Carpenter940

        another rating you might see on a 300 milliamperes device is .3A

  62. Jonathan Sturm

    I am trying to determine the polarity on my 1st Gen Kindle. Input specifications do not indicate polarity any clues on where I can go to look this up? I have already looked on amazon’s site but that detail seems to technical for the website to have.

  63. Teri

    Sorry but this is a language I don’t know. I have my Samsung Galaxy S3, on the battery it reads, 3.8 V and 7.9 Wh please someone tell me what my USB is supposed to be. Thank you for this site and forgive my ignorance in this matter.

    • James

      With new phone USB chargers 5v is standard across the board so the higher the amps you buy the better. The numbers you are reading are for the battery itself and only concern replacing the battery. Basically any USB charger will work but the higher the amps it can output the faster it will charge… at least until the phone reaches its limit. On a side note most USB charges are 1Amp so if it idoes not say that is probably the case.

  64. Jason


    I am trying to substitute two 1.5v ”D” size batteries for an AC-DC adapter. The specs of the AC-DC adapter are as follows:

    Input: 110/220V AC
    Power: 5W
    Output: 3-4.5-6-7.5-9-12V
    Current: DC 300mA

    I am using the 3 volt setting but my equipment is not operating correctly.. What mA should my AC-DC adapter have? How many watts should it be?

    Thank you for your input.

  65. Darren Purcell

    I’m late to the party here, but I just want to say thank you for the fantastic article. I have a box of over 50 power adapters and bricks of all kinds, yet I still have to go searching for the right one regularly for battery chargers, LED lights etc. Thanks to you I’ve finally labelled each one and paired them to the correct advice.

  66. Bruce

    I have an AC adapter for my gaming laptop, Alienware 17 R3, that says 180W and input is 100-240v.
    I’d like to use in South Korea where uses 220v, so is it safe to use this adapter?

  67. Cherie

    A fantastic article, which was very clear and easy to understand. Thanks so much!

    • Steve Krause

      Thanks Cherie for the feedback! Also a lot of great comments from our user community!

  68. Peter

    can anyone tell me what VAC stands for? I am looking for a 12-volt adapter amongst the hoard that I have. I am using a variable voltage device that requires 12 to 13 volts the dice allows me to reduce the power to 0 volts it is kinda like a variable voltage desktop lab but it requires an adapter to work. I have a 9volt that reads 9 volts then a solid bar over top a —- this type of symbol followed by 3VA DC. The adapter the won’t work is labeled like this 12VAC 840mA and this adapter light sup the device but doesn’t actually give me any power and i don’t understand why.

  69. Alan Moore

    What a fantastic thread you guys. I learned more than I ever dreamt about wall warts…what we call the ‘bricks” down south. Thanks to all of you, best wishes.
    Alan Moore

  70. Mary Baker

    Thank you for this excellent article and the excellent comments from people who added useful information. You just saved me and my PC.

  71. John

    Can I use iPhone charger to charge iPad?

    • Steve Krause

      Yup! iPhone and iPad chargers are interchangeable.

  72. Manuel

    Your description of polarity is a bit incorrect. It’s not whether the position of the + or – is on the left or right that determines the polarity but what sign is attached to the solid circle. If it’s the + then it’s positive polarity and negative if it’s the -. There are manufacturers, mostly from China, which displays the symbol in reverse where the “C” or open circle is placed on the right. Making a positive polarity device having the + on the left.

  73. Manuel

    220v is within the range of your device (110-240) so you should have no problem there. What you should look though is the Hz if they match. That and the W too.

  74. Manuel

    No! Though the .5v diff is rather small, it will still enough to overheat your laptop over time. If it’s the other way around (laptop 20v, charger 19.5v), you should have no problem. Your laptop will simply be under voltage but not much.

  75. Manuel

    What is the volt requirement of the device? It seems that your device is under voltage with the new adapter but enough to make it run. Your new adapter has more than enough Amp to supply though.

  76. Manuel

    It’s the difference in the Hz, I think.

  77. Manuel

    That 1.2A is the max amp that can be drawn from your adapter. Hence it will overheat if you plugged it to a device that demands higher amp say 3A. That fuse in your plug is to protect your device from sudden surge of electricity. The fuse will die in such case and you can’t turn on your device until tou replace the fuse. The fuse and adapter amp rating are unrelated. You should be fine with 5A fuse.

  78. elias

    I have question…………what if adapter provides an output both different i mean voltage and current???

  79. Zee

    Is there any difference if the polarized a circle or diamond

  80. Hally M.

    I use a white “paint marker” (available at Walmart, Menards etc.) to label my cords.

  81. Fredx

    I do like my RHINO Universal AC/DC Adaptor 1800mA. Choice of 3, 4.5, 6, 9 and 12 volts AC or DC. But the little polarity tip doesn’t lock in place. If it pulls out, read the fine print before plugging it back in. I tape mine on just in case.

    • Fredx

      I misspoke. It’s AC in DC out, not AC OR DC. Output is only DC.

  82. Aady10

    This was a good explaination and I always had a doubt with these confusing things written on adapters and other devices.

  83. pola

    Someone help me..
    I have a 10000mah powerbank that only has usb cable.

    If I buy a usb-to-dc 5v cable and connect the powerbank to a laptop with specs like this:
    Battery:6Cells 4700 mAh 50 Whrs
    Output :19 V DC, 3.42 A, 65 W
    Input :100 -240 V AC, 50/60 Hz universal

    Will it work? will the powerbank charge the battery? Will it power the laptop?

    Thank you

  84. Hadley Sevil

    Gday!! Very helpful guide thanks!! I am in Australia and have 240v power supply. The portable record player does not mention anywhere on it the desired AC power to run it although says made in Japan. Only states 9v DC. Is it possible to use a 240v power supply as long as its putting out 9v? Or best to step up/ step down like I do with my others that are stated as 110v AC? TIA still getting my head around this stuff and hope you can make sense. Cheers from Australia

  85. Khaled Budajaja

    Short and brief but very useful, I always had problem in understanding these concepts.
    Many thanks

  86. Raymond

    This may have been the closest I have been able to find anything about power supplies. My issue is well everyone in my family, phones shorting out but I don’t think its from a power supply being to hi. I think it has something to do with most don’t have a polarized plug and we don’t know what is the right way to plug it in without one. That would reverse the power of the out put wouldn’t it? I don’t know the reason I am looking into this is the cost of the equipment. Some of the plugs will get really hot so, when i notice it i quickly turn the plug but, after long term that will wear out the power supply with the chance of shorting out the device, but I have no support of this there is nothing that i can find on this. thank you

  87. Darren

    Very helpful article!

    I’ve lost the wall wart for a computer network device that requires 9V DC 600mA but my friend has the exact same device. It does not say the polarity and I can not find it online anywhere. I have a spare wall wart rated at 9V DC 1500mA that I would like to use which also doesn’t indicate polarity.

    I’ve seen references to EE type using a multimeter/voltmeter (which I don’t have) to check polarity.

    I was wondering if it would be safe (only 9V DC) to plug my friend’s wallwart into the wall, not plugged into a device, and just touch the outside of the output barrel with my hand to see if I can “feel” any voltage? If I could then it must be negative polarity, otherwise it is positive polarity. I could then repeat this on my spare power supply to see if it is the same.

    What do you think?

    • B. Carpenter

      Hi Darren,
      I have a meter so I tested your theories and this is what I found.
      1. You wont “feel” the voltage on the barrel… even when negative.
      2. Reversing the plug wont reverse the output. AC – alternating current, so the voltage is reversing into the plug anyway.

      Here’s a link to someone asking the same question :

      The speaker one, potato one and motor one are probably the easiest to do at home.

      • Darren

        Thanks for the info.

        I’ll try the potato method or grab a meter.

  88. Phil Seaman

    A great article that explains things in a simple to understand manner.

    I do however have a question based on some experience a few years ago about a device that I have coming soon.

    This is in relation to voltage stepping and equipment from around the globe.

    I once had a friend visit from the USA that was bringing her hair straighteners and purchased what I thought was the appropriate US to UK adapter but when she plugged them in, very shortly there was smoke.

    I since found out that as well as having a plug that converted US to UK, it should also have had voltage step down capability, so we bought one of the right type and all was well.

    But next week I have a device coming that also has a US 2 pin plug but is rated much lower than a set of hair straighteners, rated at 5v/2a.

    I have some universal converters that work fine with Chinese 2 pin ac adapters of the same rating but know that China uses a 220V, 50HZ system, whereas the US is 120V/60HZ.

    So my guess is that if I simply plug the US 5v/2a ac adapter into a basic plug converter that does not have step down voltage ability then the device and/or the ac adapter will be fried because there is no conversion from UK 230V/50HZ to US 120V/60HZ?

  89. Tracey

    Hi there!

    Great article by the way, very helpful.


    Recently brought and old keyboard, it came with a USA 2 pin Ac Dc Plug.

    I live in Spain , the current Input are rated at 100-240. 50-60Hz.
    In the manual for the keyboard, it only gives, “DC in 9v, 850ma” ( I worked out that it is around 7.850 W, hope I got that right!!)- So is this an output values?? It has a polarity of + Centre, -.

    The EU 2 pin plug that I have found, matches the keyboard info and the polarity. Effectively matching like for like.

    How much overpower or under power would this be for the keyboard, as regards to the rated imput? I have looked at universal plugs with adapters but have an issue with them as they are vague on differing polarities.

    To me the plug that matches seem to be right, So before I go ahead and purchase it, I would like to double check!!!

  90. Festus Guah

    Hello, I have a 19v dc output charger that only has two out cables, I need to charge it to three output cables. How can I do the changes. Please help me. It is a computer charger.

  91. John Drake

    Thank you sire for a very comprehensive guide about ac/dc adapter. i was hoping to find a replacement of my Jbl on stage III power supply adapter and i dont know which is which. but now after reading your post last night, i think i already have the idea of what kind of adapter i should look at. its 12V 1.5A positive polarity. thank you very much sire.

  92. Jenny

    This was a really helpful article! I’m wondering now how battery voltage would tie in:

    We have a white noise device that takes either 4 alkaline batteries in serial, which I know would be 6 volts, or can be plugged into the wall with a 5.5 volt AC adapter. We’ve never had (or lost ages ago) an adapter, so are looking for a cheap one at our local Goodwill, but the closest options we’ve found are 5.1 volts or 6 volts.

    Trying to think through this – if it’s rated for 5.5 volts but can run on four AAs, might a 6 volt adapter actually be ok?

  93. mirocromiro

    thanks man you saved my life!

  94. katell

    Great information!! I have a Belkin USB hub with a port for a charger but the information on the hub has not been described here yet. I have a photo but don’t know how to attach it. It is model F4U041 and the coding is something like this:
    CE; RoHS(a square icon w/check); FC (with a little c inside big C); 10 with counterclockwise arrowed circle around it; a filled in circle with check mark in it.
    Could someone decifer this for me? (yes I know these are pretty cheap and I could just buy another hub, but I’m tired of throwing things away!!!)
    Thank you to everyone who has contributed to this page, I will definitely let more people know about it.

    • Mark

      Call or email Belkin, they should be able to tell you the power specifications. I am surprised that there is no markings on it at all showing the power requirements (check next to power input and also on the botto Sidenote, these come with 3 year warranty, so also make note of this to Belkin as they may send you a replacement. They are good like that.

  95. Shanna

    Hi there, can you give me any advice as I’ve read and re-read the post but can’t work out if I should Plug this charger into my carpet sweeper or not.

    I plugged in my daughters charger to my old sweeper by accident and fried the circuits in my old sweeper, so I bought one from Ebay, only to find the stupid woman had put in a charger that doesn’t belong to the carpet sweeper. I have my old charger which is for the same brand sweeper, just a different model.

    The sweeper sticker states that it is 7.2VDC-12w
    The charger I have states that it is 6VDC-150mA

    Can I use this to charge my sweeper?

    The one the lady put with the sweeper doesn’t give the sweeper enough power, I would be better off and quicker trying to teach the dust to levitate and take itself to the dustbin! I can only use these sweepers as I have mobility issues where I can’t drag a hoover around with me.

    Any advice would be appreciated. Thanks for the giggle too, some of the comments above are very amusing.

  96. Jeff

    This was hands down the most informative, easy to understand article on the subject I have found. Thank you.

    P.S. The reason I was looking this up was to find a suitable “off brand” adapter for my blood pressure cuff. The compressor takes 4 AA batteries and runs on a 6V A.C. adapter with a polarity of inner ring(+), outer ring(-).
    Problem is I didn’t know barrel size nor amperage. Is there a way to tell amperage from the batteries required?

  97. Roberto

    My cellphone charger was indicate 100 – 240v, it is safe to plug-in into 220v outlet?

    • Mark

      Yes, this is fine. The charger is designed for this and can be use is globally.

  98. Steve

    What about AC output adapters? Do they have a certain polarity?

    • Mark

      Yes. The polarity should be noted on the adaptor label along with the Power output etc.

  99. Mrs. Anderson

    Thank you for writing this! I purchased two used RCA 25425RE1-C business phones, but one didn’t come with an adapter. Unfortunately, it looks like there’s only one real seller of the adapters, and I ordered one from ebay, but never received it, so I was wondering if I could make a universal adapter work for the phone, such as the Original Power Powerline 600 mA Universal AC Adapter found on the Walmart website (it says 3-12V DC at up to 600 mA)? On the back of the phone, it says 10V DC, 500 mA, and positive polarity. It also says use only the T-T006 DC power adapter. On the power adapter I do have, it says, Input: 120V ~ 60Hz 12W; Output: 10V (DC symbol) 500mA, and positive polarity symbol. Thanks in advance for any help.

    • Mark

      It should work fine if the Universal adaptor has the correct connectors/pins that match your phone. Just set it to 10V and ensure you have the Polarity set correctly.

  100. Mee

    So. If I have a cord that is 120v 60hz and 9w can that be used with a device that calls for 120v 60hz and 15w? And do I need to look for polarity? It’s a craig 3piece shelf clock radio stereo.

    • Mark

      Polarity is absolutely critical and if in reverse would break your clock/stereo, so always check that first.

      9 watts is not enough power and adaptor would probably get warm as your clock needs 15 watts It may work and won’t damage the clock stereo as the adaptor is lower wattage than required but best be safe use the correct adaptor to ensure you don’t overload/break the adaptor.

  101. Ginoth

    Everyone ask mostly about laptops or cellphones. Here I place something different.
    I have a car amplifier. It says 12v 5a. I suppose is standard for all car equipment.
    Now I have a new radio equipment with its own amplifier, so the now ‘old’ one, I wanna use with 2 passive speakers connected to the home projector.
    I searched everywhere home, and only find a 12v 1a adapter.
    So? Can it work?
    Also, My brother in law told me he may have a 12v 3a.
    Here’s the question: IF my brother in law has the 12v 3a… can i use it?
    If he’s mistake… can i use the 12v 1a?
    Or… should I have to find anywhere and buy a 12v 5a?

  102. KL

    I have a device rated at 29v 1.4a 60w … The AC Adapter missing..

    Can can i use 19v 4.74a 90w instead ?

    Will this harm my device?

    • MsD

      Am going out on a limb here by answering this as I am not an electrician.

      In theory, it shouldnt damage the device however good chance the adaptor will suffer. The Volts are important and generally the power required by your device. The adaptor can only give out 19volts but your device requires 29 volts. Chances are the adaptor will suffer/burn out, especially if you device requires the full 29 volts and there is a large difference between 19volts to 29volts. Dont use it.

      It would help to make note of the Device in question as it would assist in understanding the requirements.

      AMPS: are important to be always equal to or higher than required (never less) as it controls the flow rate of power to the device. It does not however generate the power so just because you have a 19v 4.74a 90w adaptor, it can never generate the 29 volts. Also: seperate to this, ensure the polarity is also correct.

      Sidenote: I will stand corrected as I am not an electrician but I wouldn’t use it.

  103. Erik

    I have A DynaDoc power station that takes 15 V but I have a charger that is a 1944. Can I use The 19 V charger on the 15 V power system?

    • MsD

      As noted on original article: The following will cause damage to your device:

      – Higher voltage adapter than device rating.

      So, no, do not us a 19v adaptor as you will damage the 15v device..

  104. Angie B.

    I use the zoom on my smartphone (S4) camera to take a close-up picture of the label on hard to read adapters.. it makes reading them a whole lot easier!..

  105. Jen

    I had a 100-240V 50/60hz input on my TV my sister gave me, and had been using a power plug that was 12V–4A, then all of a sudden, it stopped working.

    I didn’t realise the difference between AC/DC, so used an old one my sister had for a laptop and the power button goes on, but nothing comes on screen. So I wonder if because I was using a different output voltage that it could be the reason why it wasn’t working? The voltage on the adapter was lower than on the output TV.

    I’ve since ordered a correct voltage ac cord with 12V–4A, so I hope it actually works. If not, looks like it’ll be a new TV for me. :/

    • MsD

      You haven’t indicated what the TV requirements are i.e. what it says on the rear. The AC/DC part should be fine as most laptop charges handle both (it will indicate it on the power supply).
      I’ll assume the TV is 12v and requires 4amps or less based on your noted original adaptor?
      If the laptop adaptor you are now using is 12volts, and can handle 4amps or more and is the same polarity, it should work. Volts are important here and unlike a laptop, the TV will most likely require exact voltage. If you plug a 19v adaptor in, you could blow out the electronics.
      Sidenote: it may well be the TV itself is broken as there are many parts that go over time.

  106. Michael

    What Im confused about is the input amps. If the adapter says Input: 100 – 240 V (standard USA AC input voltage) and 50/60 Hz, then its the standard cycle rate of the power. But also many adapters say a maximum AMPS input. How can I control how many amps from the wall socket go into the adapter? Isnt that the job of the adapter to regulate the incoming power to the output power? I completely understand the output amps. That’s the amount of amps the adapter will put out.

  107. Michael

    In an attempt to answer my previous question but instead only to confuse the issue further, I noticed that although the AC cord connectors on several adapters consists of two figure eight female connectors. So, while the connection into the adapter is the same on several power cords, when I closely examine the plug going into the AC outlet, each cord has different specs on the actual plug. On the adapter in question which is called for 1.0 amps input, the plug on the cord going into AC wall says 10amp 120V and on this particular AC adapter cord, its printed on the female end and NOT on the AC male plug end. So, manufacture to manufacture the placement of the AC cord specifications changes. Additionally, I would note the cord has white paint with 18AWG X 2C on it as well as 300V which I assume is the wire rating for the AC cord.

    This just further complicates consumer understanding!


  108. MsD

    The Amp rating on the plug just denotes what it is capable of, eample: one wouldn’t use the same cord for a heater that is used on say a table lamp. The wiring within the cord for the heater would be thicker and capable of more throughput than the lamps. In turn if one used a lamps cord, the wires would get hot as the heater is trying to suck more power through it than the wires inside the cord can provide. One however could use a heaters cord on the lamp. Remember: Amps only denote the amount of power that can flow through. Like a garden hose…….the wider it is the more water can pass through it. Amps don’t determine the power and only control the max throughput given by the adaptor or wall socket that it is connected to. Kind of like the Water Tap controls the water (The Volts) and the hose determines how much water can actualyy pass (Amps). Not sure this helps??

    • Michael

      Yes, thank you. And that is what I assumed. But what I am also going to assume is that the adapter is giving the 1 amp input rating just to let me know that the AC plug power cord going from the wall into the adapter must bring in at least 1.0 amp. Personally, out of tons of these adapters I own with the figure eight 2 female connector plug cords, they are all higher in amps. From 6 to 10 Im noticing. Not one of them is under 1.0 amp. Im assuming that although the specification is on the adapter, there is no reason to worry about this spec. I think probably every cord that would work as far as the proper connector would carry at least 1.0 amp.

      • MsD

        Correct. To be honest, I never bother looking at the Power Cords ratings especially all the removable ones that belong to shavers, laptops, PCs, Monitors etc. Never had a problem to date.

        The exception would be if I was replacing a cord that belonged to something that used a lot of power eg. A heater, kettle, hairdryer etc. More attention is required for those to ensure the replacement is capable of handling the throughput. These type of appliences never have removable powercords so thought is required prior. An electrial store can advise on those requirements for those.

  109. MsD

    Perhaps ignore my above comment as I can’t delete it and may not be accurate or not explain well.
    This link also gives a general guide (like original thread here).

  110. Dennis

    I have a weBoost connect 4g cell/signal booster. I am using the given power adapter that has an output of 5v 2500ma. It will work for a few weeks, then the power supply will die. The unit is fine. This has happened with two different boosters and a third that was another brand/unit altogether. I’ve tried different outlets and a $300 surge protector, still lose the power supply. They’ve sent me at least 10 replacement adapters. I Even tried a different brand power adapter. Same issue. After reading your article, I’m wondering if I should try an adapter with a higher amperage rating. Thoughts? I’m desperate. Live in the sticks, have no other options for Internet and it is almost useless without the booster. Help!
    Thanks in advance.

    • MsD

      You could and having more amps than required won’t damange it as it will only draw what is required. Not sure it woukd help. though.
      Sounds like you need an electrician to check your homes wiring as that is a lot of adaptors and units.
      Surge protectors won’t necessarily protect against power fluctuations and usually only against spikes.
      Have you tried a UPS and one with power conditioning. A decent UPS provides protection against power surges, spikes and saps.

  111. Dennis

    I have not tried a ups, I will look into that. What does it stand for? Is there one you recommend? To be clear, the booster units themselves have never blown out, just the power supply units. Thank you very much!

    • MsD

      UPS = Uninterruptible Power Supply

      About: I personally can’t recommend any one device as it comes down to what is avail local to you and also your budget. APC is a well known brand.

      As you noted that you have had several replacement adaptors and also different units and all have the same issue, it may well be spikes and fluctuations in power at the socket that is causing the issue and blowing out the adaptors. A UPS that includes power conditioning and regulate voltage may help? Perhaps call the likes of APC who make reliable units for home and business and ask them for recommendations or an electrician. There are many brands and only noting APC as they are globally well known.

      Some sites that explain about UPS and Conditioning. Google around for more info.

  112. Dennis

    Thank you again. I will look into it further. I realized I actually do have a ups for my computer. I was saying surge protector, but it is a ups. Originally had the booster plugged into the wall outlet, but am having the same problem plugged into the ups. I will call an electrician. Thanks again.

  113. Bill Booth

    Power adaptor for Apple Airport Extreme. Output 12V dc 1.8a.
    Device no longer works – does work on a duplicate power brick.
    Meter shows 12volts. Is it possible for the amperage to have dropped while still maintaining the voltage?
    Curiosity – how can the layman measure the amperage?

    Enjoyed your article greatly.

  114. David McIntosh

    Your article starts out describing my dilemma almost to a ‘T,’ then never does really answer the question, how do I know which adapter will work with which device.

    If you assume that the device has no indication whatsoever of input voltage, current, or polarity, how is it possible to find an adapter which will make it work without trial and error which could also be called trial and fryer?

    Let’s face it. I’d rather fry an $8 adapter than a $120 electronic device, so if I overload the adapter, I’m not too worried about frying it. But if I put an adapter with 24VDC output into a device that requires 5VDC, I can kiss the device and my $120 goodbye.

    Is there such a thing as a (relatively) high current variable voltage adapter which is capable of furnishing (relatively) high current levels, with voltages that can be incrementally increased from very low to levels that seem to make a device operate properly? Of course, it would be a test instrument and not an adapter per se. But such a device might help a user determine what the actual input voltage a device needs without trying random power adapters and taking a chance on frying the device which it is intended to power up.

    Of course, polarity would be a factor that you’d still be taking a chance on, but many modern electronic devices have built-in polarity safeguards which are much less likely to fry because of reversed polarity than because of over-voltage.

    • MSD

      Re: If no Input voltage, current, or polarity noted.
      I have yet to see a device that doesn’t indicate this, unless a sticker was missing.
      In that case it is best to check with the manufacturer or online for the same device prior to organizing a new power supply. There would be too much guess work in most cases (for my liking).

  115. Henrique

    Hi, guys.

    First of all great article.

    Here is my situation:

    Output – 19V 3,42 A
    Input – 12V 2 A

    Will I have problems? The device is working fine (so far).

    Thanks for your help.

    • MSD

      Depends on what type of adaptor and device you are describing here. More info needed.

      If you are saying that you have a Power Adaptor that is giving out a direct 19V and you are connecting it to a device that only takes 12v, then I am surprised you haven’t burned out your device (yet). 19V is too much power and recommend you don’t use it.

      The Amps are fine as adaptor is higher than required by the device. You only need to worry if the Device needs more amps than the adaptor. Regardless: I recommend you stop using a 19v adaptor in a 12v device.

      • Henrique

        I’m using it since last Sunday. It’s for my fiber optic router (I’m not sure if it’s the right for the device). But so far is working fine.

        Anyway, as you said I’ll stop using it.

        Thanks for your feedback.


  116. Sparky

    The Zagg ifrogz 7800 power supply calls for a 1.0amp input. I bought my first one from an AT&T authorized dealer. The instructions were very brief and did not mention (nor provide) what power supply adaptor was needed! Needless to say, I soon found that the unit would not charge. Another AT&T dealer (surprising) replaced it. Same problem! Went back to the store and a very knowledgeable young man discovered that it took at least a 2.0amp charger to charge the unit. He sold me a new 2.4amp charger at cost and I’ve been happy ever since (more than 2 years)! The real solution would have been for the manufacturer to provide a charger with the unit in the original packaging. The ifrogz 7800 cost $50.

    • MSD

      I agree with what you are saying and sometimes the adaptors given especially with some Mobiles/Tablets & in this case a Powerbank are cheap and barely meet the min requirements. I am surprised that Zagg rated this as only needing 1amp. Perhaps they needed to get rid of excess!

      You haven’t indicated how many volts the adaptor is and in this case guessing it was 5V 1 amp. If so, then replacing with a 5V 2.4amp adaptor is always fine as the Powerbank will only draw as much current (amps) as it needs/capable of. I bet the original adaptor got hot as the Zagg was utilising the full 1 amp. The 2.4amp one would run cooler being under less strain.

  117. Jens Hansen

    Hi Jack. Thanks for your very useful article. I have a question that you may have answered implicitly above. I have a record player that I bought in the US. It is great and now I will bring it with me to Europe. The AC/DC adaptor has the following information on it: Input: 120 VAC 60Hz 135 mA. Output: 12VDC 500 mA. Now if I can find a plug that will work in the EU that has the same output would it then work without me burning down my house?

  118. Donald


    I have a Woodstation. This is a weather station that is made of wood that is illuminated with LED’s that actually shine through the wood laminate. Anyway, I think the DC adapter is going out. The display flickers while the adapter is plugged in but on battery power with the adapter unplugged, the flickering stops. The stock adapter is a 6V 120-240V input with a 800mAh output. The polarity is -c-+

    After searching for awhile, I found a 6V 120-240V input with 2A or 2000mAh output and the polarity is the same as noted. I think this will work fine but I wouldn’t mind a bit of reassurance. I paid about $80.00 for this thing about 7 years ago and as far as I know, they are no longer being made so I would prefer not to fry it if possible.

    Thank you

    • Brent

      Donald, your new power supply can provide up to 2amps. It will be fine for your weather station which only requires 600ma. You should not worry.

  119. Robert

    I bought a 12 volt electro-thermal cooler which came with a 120 volt ac adapter showing output of 13 volts. Will this work?

  120. Sara

    So, super simplified, if the polarity picture is the exact same on both the adapter and the device, are they compatible? I’m still if sure if the polarity drawing on the adapter is what the adapter does or what the device it’s plugged into should do.

  121. Danielle

    I have an outlet on my boat the has an output of 12v. I am trying to replace the light string that we had plugged in and I found a 12v led light string I thought would work. However, the power supply that came with it says input: 100-240v AC with output of 12v. Will this work plugged into a 12v outlet? I can’t seem to find a power supply that goes from 12v outlet to 12v light string.

  122. Allan K

    You don’t mention trickle charging. If you plug an adapter with all the correct voltage/amperage into something that was designed to have a trickle charge once it is full, you will overcharge the battery and destroy it because adapters don’t trickle charge like chargers do. Like I did with my weed whacker battery.

  123. Stepon voof

    I bought my first set of string LEDs multi colour powered by a USB, No USB supply provided. Spec on the controller out of prob China makes no sense: i.e. 12v DC input and max of 6 A output. First USBs don’t come through in 12VDC. second 6 amp is enough for a LED Christmas Tree. My finds reveal only 5V USB power supplies. Waiting to hear back from the Ebay supplier. Very Frustrating!! Stepon Voof

    • PanzerIV

      You’re right about LED strips. I’m shopping around on Amazon and so much item’s spec make absolutely no sense or are overkill. No wonder when it Chinese but they could still make an effort as for safety purpose and so we don’t buy too big amps that are more expensive, for nothing.

      Other than that, it’s by far the best and easiest to understand article about adapters and electricity :)

  124. shahzaib

    When i connect my charger to my laptop …. the battery sing on the lower left corner … start blinking with the switch sing … charging … then suddenly remove charing automaticaly and the charging …. this process rapeat again and again … fed of from this… could u plz help me

  125. Rimt

    Hi, i have 12v high torque gearbox reduction motor 15rpm,

    Will it be a problem if i use adaptor 5v 2A?

  126. Al

    If your laptop adapter is 19V 2.37 amps (=45watts) and the replacement adapter is 19V 2.1 amps (= 40 watts) is it still safe to use the replacement adapter?

  127. Abcdefg

    Hi Jack,

    Great article!

    The one thing I would add was the best tip I ever heard on the topic. Whenever you buy a device with a charger, immediately write the device info on a small piece of paper and use clear packing tape to tape it to the brick. Wrap the tape completely around the brick. This way, you always know with 100% certainty what goes where.

    • Steve Krause

      Bingo – Agree 200%. This has saved me multiple time.

  128. Betty

    We had a hurricane-related flood. My Yamaha portable keyboard and its power cord were separated during the cleanup. I mistakenly plugged in what I thought was the right cord (my masking tape marking was no longer on it), but didn’t think to check the power cord’s adapter output (24 VAC 1.5A 36VA) with the keyboard’s required input (DC in 10-12 volts) before plugging in. No music came out–just a hum. When I finally found the correctly labeled adapter and plugged it in, I still got just a hum–no music.

    Your article mentions the possibility of changing a burnt out fuse. My question: Does the fact that turning on the keyboard causes a hum mean that the fuses are not blown? Or are the operations inside the keyboard separated so that it still creates a sound even with a blown fuse? I probably could handle replacing a fuse, but hesitate to open the cover if the keyboard is likely fried even though it still makes a humming sound.

    Thanks for your blog. I found it very illuminating.

  129. Danessa

    My dog chewed on my SeaGate External Harddrive wire so now Im trying to find a replacement AC Adapter.

    Thank you for explaining everything clearly in your article and I understand its best to find a replacement that has the exact voltage and current, but I was just wondering if small difference in amps would make a huge difference.

    For Example the original adapter says Output: 12V 1.5A

    I found a spare AC Adapter labeled “Netgear Output:12VDC 1.2A” The block though is slightly bigger and heavier than the original.

    My external harddrive has ALL of my family photos so I’m afraid to even try to see what happens.

    • Steve Krause

      Yeah – I’ve had the same issue with my puppy (a few years back!).

      Really glad the article helped you get back up and running!

  130. vbn

    Power Supply (from my monitor’s manual)
    AC 100 – 240 V~ (+/- 10 %), 50/60 Hz ± 3 Hz


    Power from my desktop’s case info:

    AC 230 V 4A – 50 hhz


    Unfortunately, since i’m headless, i have mixtured ALL my power cords in a bag… i actually have 3 of them (probably one from a CRT?) so no i’m not sure which one belongs to each device…. can you help me out please?

    i have 3 power cords that say (10/16 A – 250 V), is there any problem to use any of them in any device?

    Thanks in advance.

  131. Hitarth changani


    I have a automatic Blood pressure measuring machine (bettery as well as charger). But i dont have its charger.

    On this machine near electric connection point, “DC 6V” is written.
    My dell laptop charger has same terminal (+,-) to machine. But on that nothing is written like “DC”.

    Can i use dell laptop charger for this machine charging ?

    • Steve Krause

      Hmm… My advice Hitarth, since this is medial and therefore sounds expensive, I would call the company who built the device and get them to answer the question. The last thing you want to do is plug in the wrong adapter and fry your Medical device.



  132. Ab

    From my High School Electrical Class teacher: “ALL wires contain smoke. The trick is to not let it out in the first place.”

  133. Donna

    Hi. I’m overwhelmed by all these comments. I just got an RCA 11 Maven2 Pro tablet. It comes with what I think is a charger, but I am wondering if I can use that for an AC/DC power adapter, too? I want to just keep it plugged in all the time at home. Is a charger the same thing as an AC/DC power adapter? (I’m technologically challenged, and a senior citizen, so please forgive my ignorance, and please speak ‘simply’.)
    I would appreciate a clear, simple answer.
    Thank you so much!!

    • Steve Krause

      Hi Donna,

      Power Charger/Power Adapter — Same thing. If the charger shipped with your tablet, that’s what you want to use. And yes, it’s just fine to keep it plugged in 24×7.

      Thanks Donna. Great question!


  134. Michael Morris

    MY device input 5v ___500mA and my charger output is 6vDC600mA -c+
    – – –
    Even slightly off will it mess up my my devices?

  135. Sarah C

    I’m a little confused on a different term of VA.

    The original power supply is
    Input: 120V~60Hz
    Output: 12V (DC symbol) 200mA

    Possible replacement power supply
    Input: 120V~60Hz
    Output: 12V (DC symbol) Max 1.8VA

    Is the replacement one compatible with the original?

  136. David Heap

    I have a slightly different question. I have a Sky ER115 wifi router (which works fine). In normal use, its wall adapter takes (UK 240 volt) AC mains and produces a 12 volt, 2 amp DC output. This connects via a short 1-metre cable to the router by a typical 2.1 mm centre positive male connector. In this rural area we occasionally get 2-3 hour mains power outages. Is there a simple way that I can occasionally use my standard 12 volt DC car battery for temporary backup power to the router – via a cigarette lighter connector ? I tried a simple 7 metre DC extension cable to do this. It didn’t seem to work (no power on light). Should I keep trying? Any suggestions for a simple workable solution or any issues to avoid ?

  137. vaughn

    I have a Brother P-Touch PT-2300 label maker. On the bottom of the unit it clearly states: “BATTERY 1.5V x 8, DC 12V 12W.” It’s powered by 8 AA batteries. 1.5v x 8 = 12V

    BUT on the side where the power adapter plugs in, it says: “DC IN 9.5V”

    Why the difference? Would a 12V DC adapter work? (I have a 12V adapter I could use, but I don’t have a 9.5V adapter.)

  138. Sridhar

    What is the difference between an EM and Non EM adapter?

  139. Dr General*

    Great post bro, I kept wondering what if the voltages were the same but the current is lower than the other. Because of you, I now know☺

  140. fdghdfh

    No an adapter rated for a higher current will not damage your device. The device will draw only as much as it needs, the adapter does not force more.

    For instance, a device than needs 12v at 100ma, would would work fine on an adapter that provided 12v at up to 500ma

  141. Shawn Murphy

    Do you think it’s a good idea to use a voltage meter to make sure that what the numbers say on the power supply are the same as what is really coming out of it

  142. Timothy Dobson

    This thread / Post is a keeper for answering the very confusing Power adapter replacement dillema every one faces. Thanks to all the xperts that “very concisely” explain Amp draw from devices that should be less than the Max Amp stated on Power Adapter label. The multi-volt Power adapters with switching option from voltage – 3, 4.5, 5, 6, 9, 12, etc often state little on amperage, maybe Max 3 amp. But that does not inform a non-electrical minded person if the device will work on small device. All they need to do is add a discaimer . ” Ensure your device is rated to the same voltage and to equal or below the max. amperage listed on this Adapter. The amperage output will self-adjust controlled by your device.”

    That would be enough to educate any lay person worried or simply frustrated to know if they are making a mistake,
    Great explanations from the numerous experets that piped in on this. Now I can sleep and make a knowledgable decision!

  143. JD

    I have an LG Gram 17Z990-R.AAS8U1 17.3″
    Core i7-8565U 1.8GHz 16GB 512GB laptop.

    I lost the power supply-charger.

    The original had an output of
    19.0VDC and 2.53A = 48.07 Watts

    I’ve got dozens of old power supply-chargers
    laying around and I’m hoping that one with
    a “close enough output” will work, but of
    course, I don’t want to put my laptop at risk.

    I’ve got this one:

    Lenovo MN: ADLX45NLC2A
    Output: 20VDC, 2.25A = 45 Watts

    Volts x Amps = Watts

    Will the Lenovo work without harming my LG Gram laptop?

    All replies much appreciated!

    • MSD

      Rule of thumb:
      Volts = should always be identical.
      Amps = Ensure it is the same OR greater than the original (never less) as the device otherwise the Adapter can get hot or even burn out.

      In your case being a notebook it will have some tolerance built in.
      1 Volt over (is probably fine). Amps however may be an issue and comes down to your Notebook and its requirements. Again I would say it would be fine however, if it did need 2.53amps then the Lenovo 2.25amps adapter would get hot and possible that your LG won’t get what it needs.

      A hard call but if it was mine, I would avoid it and get just but a 19V 2.53 (or greater) adapter. They don;t cost a lot on Ebay

  144. Mee Too

    Incorrect on an assertion:

    Amperage is, technically, not the rate of flow, it is the volume, or amount, of current flow.

  145. Simon

    Reading around this subject I am not sure it is quite as simple as match volts, amps at least as much as required. It seems many of these wall transformers will vary the voltage under different loads – very good ones may not but basic ones may well do. So a 5v 5amp transformer may put out at 8v for 0.5a load (in tech speak I think it’s how well regulated the transformer is). I have a 12v 0.5amp transformer that has open circuit voltage on 19v.

  146. Chris G

    Thank you for this article, and for all the comments! I am much better informed.

  147. Kathleen Smith

    Thank you so much for a really helpful article. I have a question….I am trying to find a replacement adapter for a Casio CTK-540 keyboard. I know it takes an AD-5 adapter. Can I assume that any AD-5 adapter will have the correct voltage, amperage and polarity for that keyboard? Thanks!

  148. Lenore C.

    Thank you so much for this article Mr. Busch. You saved me from burning my house down! I got a portable DVD player from Goodwill online and it didn’t include an adaptor so I guess I’ll have to buy one.

  149. ed

    what if the diagram is a complete circle in the middle? is that saying that the device internally will adjust the polarity to whatever it needs?

  150. franco Vivona

    my elliptic gym trainer LED display needs 9 v DC input , 1.5 A current. Can I use an adaptor with 9v DC and 1.0 A output?



  151. Mike

    I’m looking for a replacement adapter for a string of LED holiday lights. The adapter I need has an output of 24V and 12W, but the only similar adapter I can find is one that has an output of 29V and 12W. Would this be acceptable or should I continue looking for a better adapter?

  152. RubyRed32

    If I have an input of 12V DC 3.0A and I used a lower amp on accident will it damage the device? The output I used was 12V DC 300ma. Both have a positive polarity though. I was thinking that it was equal like 300mA=3.0A but I see now that 300mA=.3A

  153. scotty

    what if at least one, or both device and adapter don’t mention the polarities? but the dc input and outputs still match? can i just go by the in&outputs?

  154. Alengard

    First of all, what a great post! Loved it!
    Now, I have a some questions related to video games:
    My original AC Adapter for my Sega Genesis model 2 (10V 0.85A DC), so I found among my junk box (yeah, we all have one, right? Lol) a replacement (9V 0.2A DC). That said and considering the info perfectly explained on this post, I want to know if this new adaptor will harm my console?
    I am asking because on other forums, I learnt (I didn’t know) that Super Nintendos and Sega Genesis models 1 and 2 have internal voltage-current regulators which convert all power to 5V, despite the incoming power; that they could handle voltages from 3V up to 15V adaptors!
    And other guys were saying that there’s a “tolerance” range of 2V on all systems; that you can power a Sega Genesis model 2 with a 12V 1A DC without harming the console and that they have been doing that for years!

    That’s true? And consudering this, my replacement adapter wouldn’t harm my Sega Genesis model 2?

    This is one of the oldest myths on video game collecting (been collecting for 30 years now) and I want to be the one ckearing it all for the video game scene and go tell them the truth! Lol

    Thanks in advance and I’ll wait patiently your kind answers!

  155. Nico

    This article is really great! I have a Ashton Keyboard which a neighbour had given me, mainly because it wasn’t working. I decided to eliminate some possibilities. Because the speaker out put was low I thought perhaps the keyboards volume fader was on the way out. I didn’t know how to use a voltage meter, so I plug the output jacks into my amplifier and noticed it volume input
    was very low. This then drew my attention to the power supply… Voila’ the possible solution may have been found! I should have read you first because it explained everything very clearly. Thank You, Nico

  156. Geoff

    I used a 12V~1A power adapter on a device that requires 12V~3A. Is my device broken? I felt heat suddenly on my device, so I removed it from the power source. Can I still buy a 12V~3A (the correct power adapter) and will my device still work or did I break it since I used a 12V~1A prior? I was worried after reading on the “Current too Low” section of your article.

    • msd

      The Volts are right (which is the critical part) however your device needs more power then your adapter can provide. In turn your adapter will overheat and potentially burn out.
      In theory, your device should be fine and not have overheated as it was under powered. Device needs 12v 3A (36 watts) where as you are only giving it 12v 1A (12 watts). Best use or borrow a 3amp or higher adapter ensuring that is of course 12volts.

  157. David

    Can I use power supply adapter 12 VDC, 2A. To charge my supported QC.3.0 phone?

  158. Marijane Henning

    I am replacing a Hon-Kwang plug-in class 2 transformer Model A12-1830. Input: 120V 60Hz 33W, Output: 12VAC 1830 mA that came with an approx 36″ fiber optic Christmas tree with rotating color wheel. The information with the tree says, under care and use, “Do not use with a voltage converter. Use only with the indoor adapter that is provided”. I have purchased a Universal AC adapter from Belker model PA-30450W-ZMX 45W with an Input: 100-240V-1.0A 50/60 Hz. Output: 5V up to 15V = 2.2A. Polarity is positive with the + on the right. The new adapter works the 20 Watt bulb in the tree but does not turn the color wheel. What have I done wrong? Can you help me?

  159. Lori

    Great article. Thanks for writing for the non-techies out here!

    I’m confused by the parts dealing with current, though. These two passages seem to me to contradict each other:

    #1: “The following might not cause damage, but the device will not work properly:
    …Higher current adapter than device rating”

    #2: “Current too high – If the adapter has the correct voltage, but the current is greater than what the device input requires, you shouldn’t see any problems.”

    Aren’t those the same scenario?

Leave a Reply

Your email address will not be published. Required fields are marked *


To Top