A power supply system comprising a power grid input unit, an oil engine input unit, an automatic transfer switch unit, a power supply unit and a control unit, wherein the power grid input unit is configured to provide a power grid alternating current interface connecting a power grid alternating current signal and is connected to the automatic transfer switch unit; the oil engine input unit is connected to the automatic transfer switch unit and is configured to output an alternating current signal using an oil engine; the automatic transfer switch unit is connected to the control unit and the power supply unit, and is configured to, in response to an instruction of the control unit, connect the power grid input unit to the power supply unit so as to input the alternating current signal from a power grid to the power supply unit, when an alternating current is outputted normally by the power grid alternating current interface; and disconnect the power grid input unit from the power supply unit, connect the oil engine input unit to the power supply unit so as to provide the alternating current signal outputted by the oil engine input unit to the power supply unit, when the alternating current is outputted abnormally by the power grid alternating current interface; the power supply unit is configured to convert the received alternating current signal into a direct current signal, and supply power to current loads using the direct current signal; and the control unit is configured to monitor a state of the power grid alternating current interface; transmit a first instruction to the automatic transfer switch unit when it is monitored that an alternating current is outputted by the power grid alternating current interface, wherein the first instruction is used for instructing the automatic transfer switch unit to connect the power grid input unit to the power supply unit; transmit a second instruction to the automatic transfer switch unit when it is monitored that no alternating current is outputted by the power grid alternating current interface, wherein the second instruction is used for instructing the automatic transfer switch unit to disconnect the power grid input unit from the power supply unit and connect the oil engine input unit to the power supply unit; monitor currents and voltages of the current loads and a power of a current oil engine; and determine to turn off the predetermined number of current loads based on a magnitude relationship between the power of the current oil engine and power of the current loads, and priority levels of the current loads, and the system further comprising the oil engine, a plurality of loads and at least one storage battery pack, wherein the oil engine is configured to supply power to the plurality of loads when the alternating current is outputted abnormally by the power grid alternating current interface; the power supply unit is configured to act as an AC/DC device when the alternating current is outputted abnormally by the power grid alternating current interface, the AC/DC device comprises: at least one AC/DC module configured to correspond to the at least one storage battery pack and at least one of the plurality of loads, wherein each of the at least one AC/DC module is configured to convert the alternating current outputted by the oil engine into a direct current and supply power to a corresponding load in combination with the at least one storage battery pack; and a monitoring module connected to the at least one AC/DC module and configured to detect a total output current of the oil engine and transmit an instruction according to the total output current of the oil engine to control an input power of the at least one AC/DC module, such that a total output power of the oil engine is not greater than a preset power. at least one AC/DC module configured to correspond to the at least one storage battery pack and at least one of the plurality of loads, wherein each of the at least one AC/DC module is configured to convert the alternating current outputted by the oil engine into a direct current and supply power to a corresponding load in combination with the at least one storage battery pack; and a monitoring module connected to the at least one AC/DC module and configured to detect a total output current of the oil engine and transmit an instruction according to the total output current of the oil engine to control an input power of the at least one AC/DC module, such that a total output power of the oil engine is not greater than a preset power.