A power supply system (201, 301), comprising: a first power supply apparatus (211a, 311a) configured to operate independently; and a second power supply apparatus (211b, 311b) configured to supply power to a load (215, 315) to which AC power output from the first power supply apparatus (211a, 311a) is supplied, the first power supply apparatus (211a, 311a) and the second power supply apparatus (211b, 311b) being each connected to the load (215, 315) in parallel, wherein the first power supply apparatus (211a, 311a) includes a first controller (235a, 335a) configured to control an output voltage of the first power supply apparatus (211a, 311a) when power supply supplied from the first power supply apparatus (211a, 311a) to the load (215, 315) is equal to or greater than power requirement required by the load (215, 315), and to control an output current of the first power supply apparatus (211a, 311a) when the power supply is less than the power requirement, and the second power supply apparatus (211b, 311b) includes a second controller (234b, 335b) configured to stop the second power supply apparatus (211b, 311b) from supplying power when the power supply is equal to or greater than the power requirement, and to control an output voltage of the second power supply apparatus (211b, 311b) when the power supply is less than the power requirement; characterized in that the first controller is configured to change, when the power supply becomes less than the power requirement, the voltage output from the first power supply apparatus (211a, 311a) such that the voltage satisfies a first effective-value condition, and the second controller is configured to change, when the power supply becomes equal to or greater than the power requirement, the voltage output from the second power supply apparatus (211b, 311b) such that the voltage satisfies a second effective-value condition; or the first controller is configured to change, when the power supply becomes less than the power requirement, the voltage output from the first power supply apparatus (211a, 311a) such that the frequency satisfies a first frequency condition, and the second controller is configured to change, when the power supply becomes equal to or greater than the power requirement, the voltage output from the second power supply apparatus (211b, 311b) such that the frequency satisfies a second frequency condition. a first power supply apparatus (211a, 311a) configured to operate independently; and a second power supply apparatus (211b, 311b) configured to supply power to a load (215, 315) to which AC power output from the first power supply apparatus (211a, 311a) is supplied, the first power supply apparatus (211a, 311a) and the second power supply apparatus (211b, 311b) being each connected to the load (215, 315) in parallel, wherein the first power supply apparatus (211a, 311a) includes a first controller (235a, 335a) configured to control an output voltage of the first power supply apparatus (211a, 311a) when power supply supplied from the first power supply apparatus (211a, 311a) to the load (215, 315) is equal to or greater than power requirement required by the load (215, 315), and to control an output current of the first power supply apparatus (211a, 311a) when the power supply is less than the power requirement, and the second power supply apparatus (211b, 311b) includes a second controller (234b, 335b) configured to stop the second power supply apparatus (211b, 311b) from supplying power when the power supply is equal to or greater than the power requirement, and to control an output voltage of the second power supply apparatus (211b, 311b) when the power supply is less than the power requirement; characterized in that the first controller is configured to change, when the power supply becomes less than the power requirement, the voltage output from the first power supply apparatus (211a, 311a) such that the voltage satisfies a first effective-value condition, and the second controller is configured to change, when the power supply becomes equal to or greater than the power requirement, the voltage output from the second power supply apparatus (211b, 311b) such that the voltage satisfies a second effective-value condition; or the first controller is configured to change, when the power supply becomes less than the power requirement, the voltage output from the first power supply apparatus (211a, 311a) such that the frequency satisfies a first frequency condition, and the second controller is configured to change, when the power supply becomes equal to or greater than the power requirement, the voltage output from the second power supply apparatus (211b, 311b) such that the frequency satisfies a second frequency condition.