Geez.. what a load of misinformation.
First, you haven't done a TRUE NTSC conversion. Sounds like either you missed a jumper, or didn't sub the components, or you need to change the crystal.
Second, yeah 10V 1A is common as shit. But its gotta be REGULATED. A Genesis unit would do, if you could either find the connector to replace, or put a 2.1mm socket in the machine. Or use an RGB monitor/TV, yeah.
Thirdly, I don't think the PSU is auto-switching. The UK-US adaptor IS available, but you should be looking for a step-down transformer!!
Last, go somewhere like Telegames to get a spare PSU, maybe even some video leads - or does neo-geo.com sell these still?