I'm in the UK, which may make a difference, but SNES, Famicom and NES PSUs are all interchangeable.
The Famicom uses a DC PSU while the NES and PAL SNES use AC, don't they?
That's probably the confusion then; basically, in the UK, if you use a NES PSU, it will power a Famicom. The consoles themselves obviously only use DC, so if you plug a famicom PSU into the wall in the UK, it will just pop. But if you used a stepdown converter, it would happily power a NES or a PC Engine - the polarity and pin size are the right match.
I apologize for my poor wording!