A power supply system comprising a power grid input unit, an oil engine input unit, an automatic transfer switch unit, a power supply unit, a control unit and a battery pack 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 unil; 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 the 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; the battery pack unit is configured to supply power to the current loads under control of the power supply unit, and the control unit is configured to instruct the power supply unit to control the battery pack unit to supply power to the current loads; and the control unit is further 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 the oil engine; and determine to turn off a predetermined number of current loads based on a magnitude relationship between the power of the oil engine and the power of the current loads, and priority levels of the current loads. 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 unil; 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 the 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; the battery pack unit is configured to supply power to the current loads under control of the power supply unit, and the control unit is configured to instruct the power supply unit to control the battery pack unit to supply power to the current loads; and the control unit is further 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 the oil engine; and determine to turn off a predetermined number of current loads based on a magnitude relationship between the power of the oil engine and the power of the current loads, and priority levels of the current loads.