I bought one of those from Play'N'Trade for around 8 bucks. I needed it to power my Nes2, who's psu decided to freakin' die on me for no reason (screw you 任天堂株式会社,!) It also powers my black SnEs. I've had it for about 2 months and it still works and my systems haven't died yet, but I don't really play my nes2 and SnEs =P. I do spend a lot of time on my Famicom w/ Disk System addon, but that requires the opposite polarity, so it has nothing to do with the psu in question. hahaha!

This diagram will help you to not fry your Famicom with your Nes psu! Seriously! Also, you can power your Famicom and/or FDS with your TurboGrafx-16 psu; yep, the TurboGrafx-16 is that awesome!
