The motherboards for both NTSC and PAL Amigas take the same voltage. Both 110V and 220V power supplies convert to the proper voltage. Use whichever power supply you need for your wall electricity, no matter if you've got an NTSC or PAL Amiga.
Why do you want an NTSC one? I'd get a PAL one since it'll run more demos and games. You'll need an RGB monitor or a scan doubler with VGA output (like Indivision) unless you have a PAL TV lying around... but assuming you're using a monitor and not a TV, PAL is a better choice. I'm in the US and I've been using a PAL 1200 motherboard. I use a 110V power supply from my Amiga 500. The power supplies for the 500 are compatible with the 600 and 1200, but are a bit more powerful. Only really matters if you're using an accelerator, otherwise the stock 1200 power supply is OK.
