The low-voltage AC from the transformer is converted back to DC using high-current Schottky diodes (often the MBR20100 or similar). These are mounted on a large heatsink because they handle the full 30A load.
Most S360-12 units use a thermal switch or a simple transistor circuit to kick the cooling fan on only when the internal heatsink reaches ~45°C. Safety Warning s36012 power supply circuit diagram
The "hot side" of the S360-12 contains across the bulk capacitors. This voltage can remain present for several minutes after the power is disconnected. Always discharge the main capacitors before touching the underside of the PCB. The low-voltage AC from the transformer is converted