The present disclosure provides a power supply system method for an AC load (10). The system includes a power supply device (11, 21, 31A, 31B, 41) and a DC/AC converter (12, 22, 32, 42). An AC side of the DC/AC converter is coupled to an AC grid (9) and the AC load through an AC bus (8). The power supply device outputs DC electric energy and is coupled to a DC side of the DC/AC converter through a DC bus (13, 23, 33, 43). The power supply device includes an energy storage circuit (111, 211, 311, 411) and a controller (112, 212, 312, 412). The energy storage circuit includes a first energy storage circuitry (1111, 2111, 3111, 4111) and a second energy storage circuitry (1112, 2112, 3112, 4112). The controller is configured to control a conversion operation of the first energy storage circuitry to output a low-frequency power to the DC bus, and a conversion operation of the second energy storage circuitry to output a high-frequency power to the DC bus.