If you misplaced the AC adapter/power supply that came with your Nintendo NES, or it broke, you may need a replacement Nintendo NES AC adapter. Fortunately, you have a number of options.
Most devices are super picky about electricity. Don’t use random AC adapters as a general practice. What I’m about to say applies to the original Nintendo NES console, and the original NES only. I have general advice on replacing AC adapters that applies to other devices.
Unlike most devices, the Nintendo NES isn’t very picky about its electricity. Any 9 volt adapter that serves up around 1 amp (or 1000 mA) will work, whether it’s AC or DC. Polarity doesn’t matter, which is highly unusual. All that matters is whether the plug fits. I don’t know why Nintendo made this design decision back in 1985, but I’m glad they did. I wish more companies would design their stuff this way.
Your AC adapter may have gone missing over the decades. That’s understandable. It’s also possible your original adapter is just worn out. If you kept your AC adapter plugged in all the time, like most families did, your AC adapter may very well have been plugged in continuously for almost a decade. That’s more abuse than it was probably originally designed to take. Yes, AC adapters can go bad. If the original AC adapter no longer works, I’m inclined to forgive it.
Buying a new replacement Nintendo NES AC adapter/power supply
The Nintendo NES was immensely popular and remains so today. So there’s no shortage of aftermarket replacements for them, even today. If you don’t want to use a 30-year-old AC adapter that may fail, I don’t blame you for wanting something new and theoretically more reliable.
You can get a “Universal” AC adapter compatible with the NES, Super NES, and Sega Genesis that includes plugs for all of them. If you don’t want to buy online, your local game store may very well carry that adapter or something very similar. Lots of game stores still carry them. The problem is that some of these devices that supply as little as 350 mA, which is far less than the console needs. An underpowered AC adapter will overheat and stop working, and at the very least, you’ll be out your ten bucks. Also, many of them only supply 850ma, which is probably enough. But I prefer more headroom than that.
If you want to be certain you’ll get something with enough power, and don’t mind if it’s not universal, get any 9V 1A AC adapter with a 2.1mm x 5.5mm plug. Get a center negative supply if you want to use it with a Genesis too. The NES doesn’t care about polarity but the Genesis does. After you get the new AC adapter, I recommend attaching a label to it and writing on it what systems it will work with.
The upside to this approach is you’ll get a better quality power supply for your Nintendo NES, and it may cost less too.
Scrounging a replacement Nintendo NES AC adapter/power supply
The Sega Genesis AC adapter turns out to fit and work perfectly. Just be careful. The reverse isn’t true. The Nintendo AC adapter will damage a Genesis. The Atari 5200 AC adapter also works on the NES. But an original NES adapter will damage a 5200, and the 5200 adapter will damage a Genesis. So I recommend putting notes to this effect on your various AC adapters if you swap them between systems. Just attach a label, and either print or write on it what systems it’s compatible with.
I’ve used AC adapters from old modems and PC speakers to power Nintendo NES consoles with no issues whatsoever. Thousands of other retro gaming enthusiasts have done the same. As long as the specs match another console, you can use them on more than an NES as well.
If you’re a packrat and save old AC adapters even after you discard whatever they came with, look in your personal stash. You may have something suitable already. If not, pay a local thrift store a visit. Thrift stores often have a box of random AC adapters. You’ll probably find something suitable there. You may even find an original Nintendo or Sega unit. And you probably won’t pay much more than $1 for it. Look for power supplies from US Robotics modems and PC speakers if you can’t find anything with a video game brand on it. These AC adapters may not necessarily turn up as frequently as they once did, but there are plenty of them still floating around.
Imperfect matches for the Nintendo NES AC adapter
More amperage generally isn’t a problem, as long as you don’t go crazy with it. Your device will pull the number of amps it wants, and not care about a bit of excess. Using a 2-amp adapter with your NES is overkill, but won’t hurt anything. Using a 5-amp beast isn’t a great idea. An electrical fault that would be harmless with an on-spec adapter can be a problem when you have a huge surplus of amperage.
Voltage is a different story. Whether you can cheat on voltage depends on the device. The Nintendo NES is more forgiving than normal.
The Nintendo NES can theoretically take more than 9 volts. This is unusual, and don’t expect to be able to plug an overly high voltage into other systems like a Genesis. The higher you go with your excess voltage, the hotter your NES will run, and you can decrease its lifespan. So I really recommend going for 9 volts, but if all you can find is a 10-volt supply for some reason, it will work and let you get your retro gaming fix. That said, I recommend you only use it temporarily, until you find a suitable 9-volt AC adapter for your Nintendo NES.