We’ve all done it. You pull that electronic device out of your drawer, but you just can’t find that power adapter that goes with it. So, of course, you go to your box of power bricks, which really looks more like a box of spaghetti. After searching hopelessly for more time than you’d like, you finally give up, and order a new one on Amazon.

Many times when I buy broken electronics to repair, they’re missing parts. And one of the most common parts they’re missing is the power adapter. Fortunately, power adapters are easy to replace, if you know how. In this post, I’m going to save you some money by showing you how to create a replacement power adapter that you’ve lost.

The Four Main Things to Look For

When finding a replacement power adapter, there are primarily four things that you want to look for. These are:

1. The type of current (AC vs DC)
2. The voltage required by the device
3. The minimum of amount of current that the device requires
4. The polarity of the connector.

If you can find a power adapter that satisfies these four criteria, then you’ll have one that you can use with your device without damaging it.

Note: There are also some other things you can look for, such as the gauge of the wire or the type of power supply (i.e. switching vs regulated). I’m not going to cover those additional considerations in this article.

AC vs DC

You would probably guess that most modern electronics run on DC (Direct Current) power. So why even cover this topic? It’s true that most of the devices you buy off the shelf these days will be DC. However, there are devices that still may require an AC (Alternating Current) power adapter. One notorious example is the original North American Nintendo Entertainment System (NES).

When you’re dealing with digital electronics, the board itself will most likely need a DC power source, as pretty much all microchips require DC. So if you have a device that uses digital electronics, but takes an AC power source, then there’s going to be some form of a converter inside the device, such as a bridge rectifier.

Even in the cases where a device accepts AC power, you’re still going to need a power adapter to reduce the voltage down to an acceptable range. In the US, wall outlets in homes put out 120v AC. The NES power adapter, for example, steps that down to 9v AC, which the bridge rectifier inside the NES then converts to DC.

One other thing to keep in mind is that some devices that use an AC power adapter may actually work fine on DC. This depends on how the device does the DC conversion internally, and whether or not it uses the AC power for anything else inside the device. The NES, for example, actually works fine on DC power because of the bridge rectifier converts it to DC right away, and doesn’t use the AC for anything else. To illustrate, here’s a snippet of the power schematic from an NES-001 with the bridge rectifier circuit highlighted.

So, the first thing to look for when digging through your box of power adapters is to make sure that you’re giving your device the right type of current. You might be able to use a DC power supply in a system that requires AC, but never use an AC power supply in a system that requires DC. Doing so will very likely damage the device.

Voltage Requirement

The second thing is to match the power adapter with the voltage requirements of the device. For the most part, this should be an exact match of what the device requires. For example, if the device requires a 9v power supply, you’re going to need to give it exactly 9v. The components on the circuit board have a maximum voltage rating, and if you provide too much voltage it will damage them. Any less, and there may not be enough voltage for the components in the device to function.

Higher Voltage Power Supplies

It is possible that some devices will allow a higher voltage than what’s specified. Still, you shouldn’t use a higher voltage power adapter unless you understand the architecture of the device and are certain that it can handle it.

One example of this would be a device with a voltage regulator on board, which takes in an input voltage and normalizes it to a specific output voltage. For these devices, the input voltage is often expressed as a range. For example, the NES uses a 7805 voltage regulator, which takes an input voltage between 7v – 25v, and outputs a regulated 5v. So technically, you could feed in more than 9v. However, there are other things you need to be aware of.

For one thing, voltage regulators burn off the excess electrons left over from the conversion. These are usually dissipated as heat through some form of a metal heat sink. But if you don’t have an adequately sized heat sink on the regulator, the excess heat will damage the regulator. So going with the example above, you may be able to put more than 9v DC into the NES, but the heat sink on the voltage regulator was designed to handle the heat dissipation for a 9v load. If you pump in 18v, you’ll probably damage the voltage regulator.

Another thing to consider is if the pre-regulated voltage is used anywhere else in the system. Sometimes a device will split the unregulated voltage off to a different power rail than the regulated voltage. In these cases, too much voltage may damage anything leveraging the unregulated power rail.

Overall, it’s best to just match the power supply voltage with the voltage rating of the device exactly.

Determining the Device Voltage

If you don’t know what voltage the device needs, there are a couple of ways that you can figure it out. The first thing to do is to check the stickers, labels, and manuals for the device. The voltage requirements will typically be on a label under the device or written near the power plug.

If you can’t find a label, the next best thing to do is research the device online. Often times, I’ll look on eBay or Amazon for people that are selling a used power adapter for the device, and see if I can find a photo of the power adapter. From there, you can just look at the output voltage written on the brick.

If all else fails, you can usually find an online forum, subreddit, or discord channel with some enthusiasts that would be happy look at their power adapter and tell you the specs.

Minimum Current Requirement

Next, you need to make sure the power adapter you’re using can supply enough current for the load. The current capacity listed on a power adapter is the maximum it can provide, expressed in amperage.

Unlike with voltage, you can safely use a power adapter that has a larger amount of available current. For example, if the device requires 500mA, you can safely use a 1000mA power supply. The device puts a load on the current, which only consumes what it requires. You only need to make sure there’s enough current available by meeting the minimum requirements.

Connector Polarity

This last consideration only applies when you’re using a DC power adapter. Here, you’ll need to make sure that the polarity of the connector is correct. If you plug in a power adapter with the wrong polarity, it may damage the device.

When you’re using a USB-based connector or an uncommon power adapter (like on a Nintendo Wii, for example), the polarity of the connector will probably be the same on every power adapter you find. For other types of connectors, however, it may not be obvious.

Barrel Connector Polarity

One type of connector that you’ll commonly see is the barrel connector, which is used by many different power adapters.

If the center contact in the barrel connector has a positive polarity, then that’s referred to as a “center-positive” connector. And as you probably guessed, the opposite of that is “center-negative”. The outer metal casing will be the opposite polarity of the center. Because barrel connectors can go either way, you’ll always want to check the polarity before using that power adapter with a device.

If you’re uncertain about which connector contact is positive or negative in your power adapter, you can test it with your multimeter. Here’s how:

1. Put your multimeter in DC volts mode.
2. Plug the power adapter into the wall.
3. Touch the positive lead of the meter to the part of the connector that you think might be positive and the negative lead to the other.
4. If the number on the multimeter is positive then you guessed right. If it’s negative, then you got it backwards.

Usually, when a device requires a power adapter with a barrel connector, it will indicate somewhere near the power plug which polarity it requires. This will typically be a graphic that shows whether the center pin is positive or negative:

Reversing the Polarity

Sometimes, you may find a power adapter that meets the voltage, current type, and minimum current requirements, but has the wrong polarity. For these cases, you can use one of the following options.

First, you can reverse the positive and negative wires on the connector. To do this, you need to snip the wires somewhere along the cable, and solder them back together in reverse. If you do this, be sure to label this on the power adapter, so you remember that you did this when you come across it in the future.

A better (but non-free) option would be to pick up a polarity converter. This is a short cable that you can plug into the end of a barrel connector to reverse the polarity. I usually prefer this option for a few reasons:

• It’s relatively inexpensive. You can buy one from Amazon for just a few bucks.
• They’re reusable – you only need to keep a few on hand and you can use and re-use them as needed.
• They save you from mutilating your power adapters.

Finding Matching Power Adapters

With this knowledge in hand, you should now have a better idea of what to look for when digging through your bin of surplus power adapters. All the necessary information should be printed on the power adapter; you just need to match it up. Let’s walk through an example.

I recently built a Cerberus 2080 8-bit computer (I’ll have a couple of articles on that soon!). I didn’t have a power adapter for it, so I needed to find one that would work. Looking at the specs for the Cerberus, it requires a center-positive, 9v DC power adapter, with at least 500mA of current.

After digging through my cache of power adapters, I found a couple of candidates. Any of these would work, but I choose the one on the middle, which had the closest current rating (800mA).

Finding a Matching Connector

So let’s say you find a power adapter that meets the right requirements, but the connector is completely wrong. In these cases, you can acquire a connector from elsewhere, and graft it in. To help with this, here are a couple of tips for finding the right sized barrel connectors, and some ideas for what to do if you just can’t find that odd, proprietary-looking connector.

Measuring Barrel Connectors

When finding the right barrel connector, the main thing to keep in mind is that they can come in different sizes. To determine which size you need, you can measure either the connector itself or the port on the device by using a caliper.

There are three measurements you’ll need to take:

1. The outer diameter (OD) of the plug
2. The inner diameter (ID) of the center
3. The length of the barrel

Here’s a diagram of where to take those measurements on the connector:

And if you’re measuring the port, here’s another diagram of where you’ll take those measurements:

If the barrel connector you’re looking for is an uncommon size, you have no other option than to order a replacement cable. For example, this is the case with the North American Super Nintendo Entertainment System (SNES).

The SNES uses a really odd barrel connector size – 7mm OD x 1mm ID, which I haven’t been able to find for a decent price anywhere. So when I needed a power adapter for the SNES, I ordered a barrel connector adapter that’s designed to fit onto a more standard barrel connector size, and convert it to the size connector that the SNES requires. This option wasn’t free, but it was cheaper than purchasing a used or after-market SNES power adapter.

Don’t Give Up on Odd Connectors

Sometimes you might come across a device that uses an odd connector that you haven’t commonly seen on other power adapters. At first, you might think this is a proprietary connector and give up on it. However, it’s very possible that there may be other devices that use that same connector. Here’s an example that I recently came across.

This past year at Midwest Gaming Classic 2022, I picked up an Atari 7800 for a great price.

There was a catch, however – the owner lost the power adapter. Unfortunately, the Atari 7800 doesn’t use a standard power port connector. When I researched prices, replacement power adapters were going for $50 or more, which was more than I paid for the system itself. From the pictures I found of the original power adapter online, it looked like it just needed a 9V DC power adapter with 1000mA, and I had plenty sitting around that met those specs. The only problem was that I didn’t have the right connector.

After a little research, I found that the Brinkmann Q-Beam Rechargeable Spotlight had a very similar power port, and some folks in Atari forums were claiming that it fit in the socket. So, I took a risk and purchased a replacement Brinkmann power adapter from Amazon for $9… and it fit! The voltage and current on the adapter were wrong, but it was a simple job to snip off the connector and wire it into a spare 9V DC power adapter, which is exactly what I did. So, by using an old power adapter that I had laying around, and spending a few dollars to salvage a connector from a different power adapter, I was able to revive this Atari 7800 for a fraction of the price of an official replacement power adapter.

If you can’t find a similar connector for another device, there may be another option… use a 3D printer to make one! If you search around on printables.com or thingiverse.com, you’ll find that there are several people that have made 3D models of replacement connectors that you can just download and print. And if you don’t have a 3D printer, there are several online print shops that you can order a print from.

You may have to get creative and find some metal to bend into place for the contacts, but if you’re desperate for a connector and don’t want to fork over the money for a replacement cable, then this might just be the option for you.

Final Thoughts

Whew, that was a lot to cover – who would’ve thought that retrofitting power adapters could be such a vast topic. To wrap it up, here are the main take-aways from this article:

1. Don’t throw away your old power adapters… even if you lose the device they’re for.
2. When replacing the adapter, look for one that meets the type of current, the correct voltage requirement, the minimum amount of current required, and the connector polarity.
3. Don’t give up on odd connectors – do some research, and you might just find a replacement connector from a power adapter for a different device.

If you have any questions, feel free to leave a comment. I may not be able to answer it, but I’ll do my best. And if you have any ideas or suggestions for other topics you’d like me to cover, just let me know! Happy power adapter retrofitting!