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

what happens if you use the wrong 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 of different types of cell phone chargers, AC/DC adapters, power bricks, power cables, and charger plugs.

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 incredibly difficult to figure out which goes with which. The default solution to this 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. For direct currents, 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. Direct current, by nature, is a one-way street, and things just 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 that has a DC output of +12V / 5.4A. If you have a universal adapter, make sure it has the proper current rating and that you 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:

  • 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, then 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, may be okay, but it just 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, then it may run hotter than normal, which can shorten the life of the device 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, then 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 just 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.

All of the above are what you would expect to see, 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 in fact, 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!

ac-dc-mess

P.S. Wall adapters that give you a USB port for charging aren’t nearly as tricky. Standard USB devices have a voltage of 5 V dc and a current up .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 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 (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/), via Wikimedia Commons

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

  1. awraynor June 24, 2013 at 3:10 pm #

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

    • Steve Krause June 24, 2013 at 5:25 pm #

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

    • Jack Busch June 24, 2013 at 6:12 pm #

      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).

    • Murray April 30, 2016 at 2:22 am #

      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.

  2. Brian Burgess June 24, 2013 at 10:11 pm #

    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 June 25, 2013 at 1:48 am #

      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 June 25, 2013 at 8:28 pm #

      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 June 30, 2013 at 9:10 am #

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

      • stalino October 10, 2015 at 11:10 pm #

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

        • Steve Krause October 11, 2015 at 8:35 am #

          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 October 13, 2015 at 5:44 pm #

            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 July 17, 2016 at 9:12 am #

        LOL!

  3. Elaine July 13, 2013 at 5:07 pm #

    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 January 9, 2016 at 8:10 am #

      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.

  4. Caitriona June 4, 2014 at 1:48 am #

    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 December 27, 2015 at 3:55 am #

      CHECK INSIDE THE APPLIANCE THERE MAY BE A FUSE WHICH BLEW

  5. Denz July 13, 2014 at 10:55 pm #

    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 September 4, 2014 at 8:40 am #

    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 September 16, 2014 at 4:24 pm #

      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 September 16, 2014 at 4:33 pm #

      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.

    • Kelly March 16, 2015 at 11:47 pm #

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

      • Francesco March 30, 2015 at 9:14 pm #

        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 December 29, 2015 at 2:46 pm #

      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?

      thZ.

      • EmilN February 25, 2016 at 1:25 am #

        @MikeM
        “-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 November 29, 2016 at 10:21 pm #

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

  7. dan September 10, 2014 at 6:41 am #

    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 October 9, 2014 at 11:26 am #

    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 September 14, 2016 at 3:35 am #

      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 October 15, 2014 at 3:39 pm #

    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 November 5, 2014 at 8:03 am #

    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 December 10, 2015 at 11:19 am #

      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 November 25, 2014 at 2:57 pm #

    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 December 9, 2014 at 1:32 am #

    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 December 10, 2014 at 4:37 am #

    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 December 27, 2014 at 9:04 am #

    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 January 13, 2015 at 4:06 pm #

    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 October 23, 2015 at 7:04 pm #

      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 February 18, 2015 at 3:25 pm #

    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 August 22, 2015 at 5:39 am #

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

  17. dawn February 27, 2015 at 6:32 am #

    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 March 4, 2015 at 1:19 am #

    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 March 8, 2015 at 4:10 pm #

    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.

    -Tim

    • Some Bro January 8, 2016 at 6:14 pm #

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

  20. Al C March 20, 2015 at 8:59 am #

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

    • Carpenter940 May 4, 2016 at 12:55 pm #

      Positive is the one with the stripe

  21. daemon April 8, 2015 at 7:54 pm #

    excellent article.

  22. Steven April 10, 2015 at 7:23 pm #

    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 April 18, 2015 at 2:12 am #

    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 May 4, 2016 at 12:57 pm #

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

  24. G J BUNTON May 9, 2015 at 12:11 pm #

    Hello,
    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 May 19, 2015 at 4:53 am #

    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 December 10, 2015 at 11:31 am #

      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 June 1, 2015 at 8:30 am #

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

  27. Matrix June 6, 2015 at 10:47 am #

    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 July 14, 2015 at 6:25 pm #

    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 January 8, 2016 at 9:22 pm #

      Don’t do it! You’ll ruin it.

    • EmilN February 25, 2016 at 1:33 am #

      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 May 4, 2016 at 1:00 pm #

        I second EmilN’s comment

  29. cindy August 5, 2015 at 9:16 am #

    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 September 6, 2015 at 10:52 am #

    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 October 18, 2015 at 1:43 pm #

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

  32. Chuck October 22, 2015 at 2:17 pm #

    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 November 6, 2015 at 9:13 am #

    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 November 8, 2015 at 10:54 am #

    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 November 11, 2015 at 3:56 pm #

    @ 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 November 21, 2015 at 9:49 pm #

    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 November 24, 2015 at 6:54 am #

      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 November 24, 2015 at 6:52 am #

    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 December 5, 2015 at 5:50 am #

    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!!!!!

    YES I WAS ASTONISHED.

    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 December 10, 2015 at 11:41 am #

      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 December 19, 2015 at 1:52 pm #

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

    • Matt December 19, 2015 at 7:43 pm #

      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 December 20, 2015 at 2:04 am #

    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 December 30, 2015 at 8:57 am #

    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 December 30, 2015 at 9:08 am #

    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 December 30, 2015 at 9:18 am #

    Matt,
    Very reasonable. Please reach out at your convenience: jayaallen * gmail.com.

  44. rony January 5, 2016 at 5:29 am #

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

    • Matt January 5, 2016 at 8:58 am #

      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 January 5, 2016 at 7:00 pm #

    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 January 10, 2016 at 7:31 pm #

    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 January 19, 2016 at 11:01 pm #

    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 January 20, 2016 at 10:19 am #

    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 January 29, 2016 at 9:20 am #

    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 February 1, 2016 at 7:06 pm #

    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 February 13, 2016 at 4:58 pm #

    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 February 18, 2016 at 11:17 am #

    HI
    I HAVE A ALESIS MIXER WHICH SAYS 18V5OOmA
    POWER ADAPTER OUTPUT :AC 17X2V0.84A
    PLUGED IT IN AND ALL LIGHTS CAME ON BUT DIDNTRUN THE UNIT

  53. joyce March 4, 2016 at 5:53 am #

    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 March 5, 2016 at 5:52 am #

    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 May 4, 2016 at 1:13 pm #

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

  55. Mike Fredrick March 5, 2016 at 9:38 pm #

    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 March 22, 2016 at 6:40 am #

      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 March 8, 2016 at 10:19 am #

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

  57. Dave March 9, 2016 at 12:19 pm #

    – – – – – – –
    _______

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

  58. Norm March 10, 2016 at 2:45 am #

    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 March 22, 2016 at 6:03 am #

    This was really helpful thank you.

  60. doh March 25, 2016 at 1:21 am #

    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 March 25, 2016 at 6:08 am #

      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 May 13, 2016 at 3:07 pm #

        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 March 31, 2016 at 6:52 am #

    What does the m mean in 300mA for example?

    • Steve Krause March 31, 2016 at 9:01 am #

      Milliamperes. So 300mA = 300 milliamperes.

      • Christine March 31, 2016 at 10:27 am #

        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 May 4, 2016 at 1:19 pm #

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

  62. Jonathan Sturm April 9, 2016 at 7:02 pm #

    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 April 20, 2016 at 11:04 am #

    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 April 25, 2016 at 6:54 pm #

      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 April 30, 2016 at 12:36 am #

    Hello,

    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
    60/50Hz
    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 May 9, 2016 at 3:30 am #

    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 May 9, 2016 at 8:04 pm #

    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 May 10, 2016 at 10:02 am #

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

    • Steve Krause June 3, 2016 at 2:59 pm #

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

  68. Peter May 29, 2016 at 11:33 am #

    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 June 2, 2016 at 8:20 pm #

    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 June 9, 2016 at 4:04 pm #

    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 June 12, 2016 at 4:24 am #

    Can I use iPhone charger to charge iPad?

    • Steve Krause June 12, 2016 at 10:20 am #

      Yup! iPhone and iPad chargers are interchangeable.

  72. Manuel June 30, 2016 at 8:29 pm #

    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 June 30, 2016 at 8:37 pm #

    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 June 30, 2016 at 8:57 pm #

    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 June 30, 2016 at 9:08 pm #

    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 June 30, 2016 at 9:13 pm #

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

  77. Manuel June 30, 2016 at 9:29 pm #

    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 July 5, 2016 at 10:45 pm #

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

  79. Zee July 16, 2016 at 8:22 am #

    Is there any difference if the polarized a circle or diamond

  80. Hally M. July 22, 2016 at 1:49 pm #

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

  81. Fredx July 23, 2016 at 7:40 am #

    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 July 23, 2016 at 7:44 am #

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

  82. Aady10 July 25, 2016 at 11:56 am #

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

  83. pola August 17, 2016 at 8:56 am #

    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 August 25, 2016 at 3:15 pm #

    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 September 6, 2016 at 7:07 am #

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

  86. Raymond September 11, 2016 at 1:21 pm #

    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 September 14, 2016 at 10:58 pm #

    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 September 15, 2016 at 1:12 pm #

      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 : https://electronics.stackexchange.com/questions/42374/ways-to-determine-polarity-dc-without-a-meter

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

      • Darren September 15, 2016 at 3:58 pm #

        Thanks for the info.

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

  88. Phil Seaman September 17, 2016 at 6:09 pm #

    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 September 20, 2016 at 9:03 am #

    Hi there!

    Great article by the way, very helpful.

    EEK!!

    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 September 22, 2016 at 1:16 pm #

    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 September 27, 2016 at 5:58 pm #

    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 October 11, 2016 at 8:54 am #

    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 November 19, 2016 at 4:12 am #

    thanks man you saved my life!

  94. katell December 1, 2016 at 6:58 am #

    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 December 9, 2016 at 3:42 pm #

      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.
      Cheers

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