read up on any article about how to "build a supergun" with a PC power supply -- it can be done, yes, but PCs run different amperage on the various power rails that's much higher than what's found in an arcade power supply.
it can be done, but you have to add fuse blocks in-between, because if there's ever a current spike, it could nuke your PCB. be that as it may, they're not a reliable source of power for what we're doing here, they're just an option in a pinch.
I think the only application where they're OK to use as an arcade replacement is with the Sega NAOMI/NAOMI 2