Schematic: A20112 Power Supply

The A20112 is a switch-mode power supply (SMPS) designed for the Namco System 246 and 256 arcade motherboards. Unlike standard PC ATX power supplies, the A20112 utilizes a custom form factor and a dedicated single-row output connector to interface directly with the arcade I/O board. It is a high-efficiency unit capable of delivering substantial current on the +12V rail to power the console's cooling fans and disc drives, while maintaining stable low-ripple voltage for the sensitive CPU and RAM (+3.3V and +5V).

that need a "set it and forget it" power source that won't interfere with sensitive signals. a20112 power supply schematic

: If the main capacitor voltage is only ~320V DC (on 230V AC input) instead of ~390V–400V, the PFC stage controlled by the A20112 is likely not starting. The A20112 is a switch-mode power supply (SMPS)