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I bought an SNES recently, and it came with a aftermarket power supply. Is this one at the correct amperage, etc.?

Input: AC 120V 60Hz; Output: DC9V - 850mA

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  • 10V at 850mA is 8.5W. 9V at 850mA is 7.65W. If any game or whatever you run on the NES that requires more than 7.65W you'll (maybe, probably, or maybe not) experience a failure. This means that the NES is working hard - think games that use the NES CPU and RAM (etc.) a lot. However, it's likely that's it's ok for most games. Also, specs usually include some buffer and will likely work over the rated spec. Or not, it might catch on fire, burn your house down, and kill your spouse. Depends on quality and manufacturer.
    – Steve
    Commented Jun 25, 2022 at 7:14
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    @Steve: You're assuming a switching power supply that will draw constant power from an input of varying voltage. As Hearth pointed out, a 1991 design likely used linear regulators and would draw constant current of any voltage sufficiently above 5 volts (but not so high that it overheats the regulators.)
    – Peter Cordes
    Commented Jun 25, 2022 at 10:45
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    "You can't use any old 9v supply you've got lying around the house because the SNES uses a center negative pin which is the opposite of the de facto standard today. Best case is simply nothing happens, worst case it bricks your SNES. A 3rd party adaptor that's advertised for SNES is not likely to break your SNES, but you might have weird visual artifacts or other glitches." reddit : is_9_volts_enough_to_power_the_snes
    – Mazura
    Commented Jun 25, 2022 at 19:25
  • @PeterCordes yeah ... It regulates it to a constant 5 volts. Any headroom anove that goes to power supply current capability, which is determined by the needs of the device being powered .. until it can't provide any more, then undesirable things happen. I too am an electrical engineer, and my comment does not disagree with that answer.
    – Steve
    Commented Jun 26, 2022 at 15:39
  • The linear regulators don't draw constant current. They provide a constant 5v, the current changes depending on the load ... Idle sleep loop? Low power. Lots of graphics and sound processing work a coprocessor in the cartridge? More current. Regardless of supply. 5v , always. Well ... Technically when you overload the supply, the voltage will also likely drop below the rated voltage. I think your understanding of voltage and current regulation isn't fully correct. The entire point of a voltage regulator is to regulate voltage, one of the three parts of ohms law.
    – Steve
    Commented Jun 26, 2022 at 15:43

2 Answers 2

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I just went and checked the power supply on my SNES (an original Nintendo power supply)--it's 10 V at 850 mA. Your supply is slightly lower voltage.

Speaking as an electrical engineer with some familiarity with how circuits were designed in the 80s and 90s, it's very probable that 9 V is enough. (current rating doesn't matter as long as it's high enough, by the way--the power supply could be rated to 10,000 A and it would work just fine. Though I'd question why you're using such expensive specialist lab equipment to power an SNES, if it was!)

Most of the SNES (and most 80s and 90s electronics) runs on 5 V, and there's an internal voltage regulator (most likely a linear regulator) that drops the input voltage down to 5 V. There may be some parts of it that run on 9 V (another standard voltage) as well, but that seems unlikely to me--the voltage regulators readily available at the time would typically require at least about 11 V to output a stable 9 V, and while ones that could drop 10 V to 9 V existed, they wouldn't have been as cheap as just using a higher voltage power supply.

It's also possible that some nominally 9 V parts are being run at 10 V straight from the supply; some things are perfectly happy on a pretty wide range of voltages. In that case, your 9 V supply would also be perfectly fine.

In any case, I wouldn't worry about it. Even if it turns out not to work, it's extremely rare for something to break from applying too low of a voltage. Too high a voltage can cause damage easily, but it takes some weird edge cases for too low a voltage to do any damage at all.

Do be aware, however, that low-quality power supplies can fail in ways that will damage things. If the power supply is working properly, everything's fine, but if it breaks, in the worst case you could end up passing mains voltage through to your SNES, which absolutely will fry just about everything on the board. Might be a good idea to replace it with one that's a little better quality; there are aftermarket ones out there that look a lot less sketchy than this one.

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    Looked at the schematics and they do create a filtered 9V from the 10V, which will now be 8V. This is used for the audio OP-amps and buffers in the lower right section, and there's still enough headroom with 8V. In summary - this answer checks out.
    – pipe
    Commented Jun 24, 2022 at 16:28
  • As someone with knowledge, you could probably improve this answer with a warning about low-quality power supplies. I can't truly tell from the photo, but OP's PSU doesn't strike me as a quality unit.
    – jaskij
    Commented Jun 24, 2022 at 16:30
  • @pipe I'm surprised, I would have thought in the early 90s they wouldn't have used 1 V dropout in a design, even if they had a 1 V dropout LDO. But yes, 8 V is still going to be plenty to run the circuitry. It won't be properly filtered, though, since whatever regulator they use will be operating in dropout. That won't cause any problems; you might just have a bit of audio noise.
    – Hearth
    Commented Jun 24, 2022 at 17:45
  • @jaskij You have a point. I'll add some.
    – Hearth
    Commented Jun 24, 2022 at 17:45
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    @pipe Oh, I see where it's generated (top right of that schematic). It's just filtered, not regulated.
    – Hearth
    Commented Jun 24, 2022 at 17:54
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I'm assuming you're referring to the NTSC SNES released in 1991, due to the power supply being rated for 120V 60Hz, and due to asking about the SNES and not the Super NES Classic Edition (also known as SNES Mini).

Judging by an image found on an iFixit article for SNES outer case replacement (NTSC version) (click for larger version):

Bottom view of US SNES

The NTSC SNES is rated for 10V at 850mA. Meanwhile, your power supply outputs 9V at 850mA. While it does have the correct amperage, it is short 1 volt.

Unfortunately, I can't answer whether or not this might cause any problems, and what these problems may be.

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    Knowing the technology landscape in 1991, 9V instead of 10V will probably make it only run a bit colder. From the picture, the power supply looks like transformer-based (in 1991 a switching power suppies were neither common nor cheap), so it is at least as unstable as your utility voltage (e.g. +/- 10%) anyway. It may fail to work if the socket voltage is at minimum, but not to the point of breaking.
    – fraxinus
    Commented Jun 24, 2022 at 16:21

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