Power Supplies

One hundred forty-seven dollars and thirty-nine cents—that is the cost for replacing a power supply for an old MiniITX computer system I found in my office. Mind you, the entire unit cost about $199, and that was five years ago, but still, the cost for a replacement power supply is absurd.

Thankfully, a quick search on the Internet found a universal power adapter that fit my requirements for about $18. How can you find inexpensive replacements for your missing power supplies, without frying your vintage arcade cabinet computer? There are a few important things to watch for:

  1. Voltage: most universal power adapters have several voltage selectors; make sure that they match your needs. (For example, laptop power supplies generally require more voltage and, unfortunately, are more expensive.) The device should say near the power adapter how much voltage it requires. The network switch in Figure 1 shows a need for 7.5V of DC current. Some devices require AC voltage as opposed to DC, so be sure to look for “DC” on the device.

  2. Amperage: your device generally will say near its power port the amperage it requires along with the voltage. Amperage is a little different from voltage, and you want to make sure your power supply supplies at least as much amperage (usually measured in milliamps) as your device requires. The device will draw as much amperage as it requires, but there's no concern if the power supply gives more than it requires. The network switch in Figure 1 shows a 1 amp minimum requirement.

  3. Polarity: your device most likely will have a drawing that shows whether the tip of the plug is positive and the jacket negative, or vice versa. Most universal power supplies will have a selector that looks similar. Make sure polarity is lined up! It's just like putting batteries in backward if you flip the polarity.

  4. Plug: I wish there were a standard for the various types of plugs you might face, but sadly, there's not. Most universal adapters come with a selection of plugs that will fit most devices, but unfortunately, not all. It is possible, if you feel a bit adventurous, to cut the end off your old power adapter (assuming you have it) and solder or tape the correct plug on the wire of the universal adapter. Be warned, however, that it's easy to mess up polarity when you do that.

There are some other factors to weigh in as well. Some cheap universal power supplies are not regulated, which means they can vary in voltage depending on the load they're put under. If your device is particularly sensitive, you may want to watch for that. In the end, if you're worried you might mess up and ruin your prized powerless device, you always can shell out the $147.39 and get a new one. For me though, $18 was more in my budget.

Figure 1. This network switch shows a need for 7.5V of DC current.

Figure 2. Associate Editor Shawn Powers wrangles with his power supplies.

Shawn is Associate Editor here at Linux Journal, and has been around Linux since the beginning. He has a passion for open source, and he loves to teach. He also drinks too much coffee, which often shows in his writing.

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