Power supply system and power supply unit

The purpose of the present invention is to synchronize two or more power supply units constituting a power supply system and to stably operate the power supply system. A power supply system (100) provided with two or more power supply units (10-13) that supply DC power to a common load (22) in cooperation, the power supply units (10-13) being provided with: a power supply main circuit (30) that converts AC power input from the outside into DC power; a control unit (36) that controls the power supply main circuit (30); a pair of synchronization terminals (Z1, Z2) respectively connected to the pair of synchronization signal lines (ZCL); a transmission unit (35) for conducting between the pair of synchronization signal lines (ZCL) and outputting a trigger signal (TG); and a reception unit (35) that detects the conduction state between the pair of synchronization signal lines (ZCL) and receives the trigger signal (TG), and the power supply main circuit (30) starts output on the basis of the reception timing of th