I have a box of miscellaneous power supplies / AC adapters / transformers / "bricks" which have no information on them about what they are for. I am trying to match them up to the devices they belong with, including computer items, drives, cameras, and who-knows-what else. Some of the devices may have already been discarded.

Sometimes I have been successful typing the model numbers into Google, but usually I just get nothing, or maybe a list of places to BUY the adapter. With some, I am told they are for a camera, for example, and that narrows down my search.

Does anyone have tips for identifying them? Wouldn't it be nice if there was a website with some sort of cross-matched list for these things?


  • Sino-American Model A30980 AC Adapter Class 2 Transformer;
  • Ambico 45-8820 Class 2 Transformer Model 35 - 7.5 - 300C;
  • AC Adapter (No Brand) Class 2 Transformer Model No. DBU120020
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    \$\begingroup\$ No help to you, but I mark every adapter with a label maker when it comes in. Sometimes the voltage and polarity is marked on the product- it's always marked on the adapter- that can help matching them up. \$\endgroup\$ Commented Sep 23, 2014 at 5:21

1 Answer 1


Rarely does the manufacturer of a given device also manufacture its AC adapter. Therefore you really have nothing to go by except matching:

  • Voltage: The adapter must provide the DC (or AC) voltage required by the device; no more, no less. (Or if you have to, ideally no more than ±10%.)

  • Polarity: The tip and sleeve (inside and outside of connector) must be the correct polarity. This is usually indicated by the symbol:

    DC polarity symbol

  • Current: The adapter must provide at least the current required by the device.

  • Power jack dimensions: DC barrel jacks are not all the same dimension. If you find a suitable adapter for a given device, you might find the plug doesn't fit the jack.

Things that will hinder your efforts:

  • Some adapters may not be labeled. Use a multimeter to measure output voltage and polarity.
  • Some adapters are not regulated, meaning they were intended to provide the specified current only for a particular load. Thus, a "12V 500mA" adapter might measure 18V or more with no load. If you power a device that requires less than 500mA, it may provide a voltage that's too high.
  • Some devices aren't labeled. Try searching online to determine the correct adapter, but be warned that the incorrect polarity or voltage could damage the device. If it wasn't labeled, it probably deserved it. :)

Please read Olin's question and answer about selecting the correct power supply for more information.


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