You have an A.M.O.A. standardized power supply made for certain JAMMA cabinets like some Dynamo conversion cabinets, some Konami cabinets, and some NeoGeo cabinets. It really is an old XT computer power supply made for amusement game use.
This power supply needs an external on-off power switch (double pole single throw, DPST).
Pinout is as follows:
The cable terminated in a 4 pin Molex connector is the power switch cable. You will need to connect a DPST toggle switch to this connector or two jumper wires in the connector to turn the power supply on. Pin 1 should be jumpered to pin 3. Next jumper pin 2 to pin 4.
The cable terminated in a 3 pin Molex connector is the switch controlled AC 120 volt output to the cabinet isolation transformer and fluorescent marquee light fixture. Pin 1 is AC Hot (black), pin 2 is earth ground (green), and pin 3 is AC Neutral (white).
The cable terminated in a 9 pin Molex connector is the DC output to the gameboard. Pins 1, 2, and 3 (usually red color) are +5 volts. Pins 4, 5, and 6 are ground (usually black color). Pin 7 is -5 volts (wire color may vary from model to model). Pin 8 is +12 volts (wire color may vary from model to model). Pin 9 is empty and not used.
These power supplies MUST HAVE A LOAD CONNECTED (to the +5 volts) to operate properly.