A power supply apparatus including: N+m power source conversion modules, where N power source conversion modules are main power source conversion modules; a power source conversion module includes a detection and switching unit and a conversion unit, where the detection and switching unit is separately connected to an output end of a first alternating current power source and an output end of a second alternating current power source, and the detection and switching unit is configured to monitor in real time a working state of the first alternating current power source and a working state of the second alternating current power source, close a channel between the conversion unit and one power source, which is in a normal working state, of the first alternating current power source and the second alternating current power source.