The following info was kindly contributed by our forum member Arcade
X68000 has inverted power-on signal and Power Supply Replacement suggests using an invertor IC (a 74HC04) and a resistor (4.7k Ohm) with the replaced power supply. For a smaller solution and less soldering you can use 2N7000 N-channel MOSFET instead. Connect 'source' to ground, 'drain' to the ATX 'PS_ON#' pin, and then the yellow wire from the X68K to 'gate'.