The present disclosure provides a power supply system method for an AC load. The system includes a power supply device and a DC/AC converter. An AC side of the DC/AC converter is coupled to an AC grid and the AC load through an AC bus. The power supply device outputs DC electric energy and is coupled to a DC side of the DC/AC converter through a DC bus. The power supply device includes an energy storage circuit and a controller. The energy storage circuit includes a first energy storage circuitry and a second energy storage circuitry. 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.