US models use 9v AC and 1.3 amps. You'd be better off trying to find a compatible transformer that runs off US outlets. Of course, you could pick up a voltage adapter, and run your NES from there, but from my experience, adapters are unreliable and only work with heaters. NTSC units also run at a slightly faster clock speed, but it probably shouldn't matter. Most games are not timing oriented. By the way, you may want to make your nes region free if you haven't already.
Here is a good textfile on system region compatibility.
"Good lord, Lois, either I was a C section, or you're wonder woman!"-Stewie
