Its super simple to convert an ATX psu for use in an Amiga. Just cut the green wire and one of the black wires and short them, preferably with a toggle switch between them (This will be your on/off for the computer). Then cut the power plug from the Amiga PSU (the one that plugs into the Mobo), leaving several inches of wire to work with. Remove the corresponding connector from the ATX PSU and discard. Now simply connect your Amiga connector to the wires of the ATX PSU making sure the voltages go to the right wires on the Amiga power plug. There's just a few wires you'll need. +12v, -12v, +5v and Ground.. Thats it. Just cap and tie the remaining wires out of the PSU and install it in the Amiga. Might want to check your output voltages first with a meter and make sure +5v is going to +5v, and +12v is going to +12v, etc..