A power supply system having a plurality of power systems is provided with a power output section in each of the power systems, an electrical load in each of the power systems, operating from power supplied by the power output section, main paths that connect the power output sections of adjacent ones of the power systems, an inter-system switch that establishes a conducting condition between the adjacent power systems by being turned on and establishes a disconnected condition between the adjacent power systems by being turned off, and an intra-system switch in each of the power systems, which is disposed on the main path between the power output section and the inter-system switch, and which establishes a conducting condition between the power output section and the electrical load by being turned on and establishes a disconnected condition between the power output section and the electrical load by being turned off.