This game cabinet used a modified IBM XT computer style power supply. It was modified to JAMMA wiring standards for use in commercial coin-op video games. The 9 pin connector is for the DC output from the power supply. There is a 3 pin connector that comes out of the power supply with black, green, and white wires in it. This is the AC output from the power supply and plugs into the mating connector on the isolation transformer. A similar power supply was used in dedicated Neo-Geo games.
Visit
www.happcontrols.com and look at these 3 power supplies as one of them will be the one you need to buy:
80-0072-00 (uses an external power on-off switch thru the 4 pin connector dangling out the power supply)
80-0015-00 (has the power on-off switch built into the case)
80-0002-10 (has built-in power switch and can operate with an external power switch; has extra connector for +5 & +12 volt accessories like disk drives, etc.). I think this is the one you need.