Power supply system and power supply method

A power supply system is adapted to supply a power to a load, is connected to a load sharing bus, and includes two power supply devices and a control device. The two power supply devices are connected in parallel to the load, respectively have a maximum power, and respectively output an output power to the load. The control device is electrically connected to the two power supply devices. When a controlling condition is met, one of the two power supply devices with the greatest maximum power adjusts the output power according to a controlling signal from the control device and a sharing signal from the load sharing bus, so that the two output powers of the two power supply devices are the same or similar.