Nes systems are surprisingly unpicky about power.  They are one of the few electronic items that expect AC power from the wall wart, so they don't care which way the positive or negative are.  Also you can throw them a decent amount higher voltage, and it won't matter either. 

I have no clue if the the famicoms expect AC or DC or what voltage it expects.  Maybe if somebody can read what it says on their famicom's AC adaptor, you can just find something close.  Where are you now?  Don't just get a prong converter if you're in the US.  It expects to run on 220, not just that it has different prongs...

Where do you live JC?  The incoming 220 or 110 doesn't really matter.  It's just that if it's expecting 220, it has a different transformer than if it's expecting 110.  It then "transforms" the 110 or the 220 into the proper volts/amps.  If you want to use your 220 plug on 110, you need a step up converter:

http://www.action-electronics.com/trnsupdn.htm

They're not cheap!


It will probably be easier to find an ac adaptor that will work with it, What does your 220 generic famicom adaptor say on it?  Does it have the output volts and amps?  Does it have a picture like this with the + and -:

?----C-----?

That sounds like what a SNES adaptor outputs if I remember correctly.  Double check to see if it matches including making sure the  (+)---C---(-) is the same.  Then try it if it fits.

Yeah, Michael, that's what I was thinking too...SNES adaptor is 10V, and NES is like 10.5?  There is a difference, because I freeped my SNES using the NES adaptor by accident.  

If the voltage on the SNES adaptor is the same (10V DC) and the power supply will supply at least as many mA as the original (850 mA or more), then he can buy a cheap center-negative gender changer at Radio Shack (I think) if the polarity is wrong.

The NES adaptor may not be able to supply enough mA to get the system started, or the Famicom might just not run at all on 10.5V.



(BTW, To "freep" in my language is to turn on a game system and get that really mean buzzing sound accompanied by a mostly black screen but with one thick, bright white bar of static noise across it.  It usually means something is seriously wrong with the power supply or the wrong one is installed, such as me getting the two adaptors switched on accident).



EDIT:  You might be able to run the Famicom even if the SNES adaptor is rated for less than 850mA.  It may not even run the Famicom, but if it does, leave it on for an hour and check often to make sure that the adaptor is not getting too hot.  Warm is ok, but if it starts getting really hot, then the Famicom is pulling more current than the adaptor is designed to provide, and among the tragedies that could occur:


1) The wires melt, creating a short circuit which fries the system and the adaptor.

2)The adaptor casing melts, creating a situation where you have an exposed-coil transformer plugged directly into mains power and no way to remove it from the outlet.

3) The adaptor goes "pop" and then stops working.  Most likely, you blew the internal adaptor fuse, which is designed to make the adaptor idiot-safe so it can get the little "UL" logo.

4) The adaptor goes "pop" and then your Famicom, and probably your carpet, catches fire.  This scenario is the most dire - a failure in the power adaptor could  theoretically cause direct 120V AC current to be fed down the wires right into your Famicom.



So just be careful, and if you think you are pulling more mA than it was designed for, give it a test run for an hour.  Temperature of the adaptor is the main thing.