A power supply system comprising: a low-frequency transformer power supply operable in a high-power state; and a switching power supply operable in a low power standby state, wherein the switching power supply includes a first switching element connected between a primary winding of a transformer for the switching power supply and a ground, a rectification smoothing circuit (D0005, C0004, L0001, C0002) connected to a secondary winding side of the transformer for the switching power supply, an output voltage detection circuit configured to detect an output voltage value of the rectification smoothing circuit (D0005, C0004, L0001, C0002), a photocoupler configured to transmit the output voltage value to a control circuit that is configured to control the operation of the switching power supply, and a second switching element configured to receive a stop signal for stopping operation of the switching power supply, in order to provide for a transition from the low power standby state to the high-power state, characterized by the switching power supply further including: a photocoupler drive circuit (102, 104, 106, 110) configured such that when the second switching element has received the stop signal, in order to provide for a transition from the low power standby state to the high-power state, power output from an operating one of the low-frequency transformer power supply or the switching power supply is supplied to the photocoupler, and the stop signal for the switching power supply is transmitted to the control circuit via the photocoupler. a low-frequency transformer power supply operable in a high-power state; and a switching power supply operable in a low power standby state, wherein the switching power supply includes a first switching element connected between a primary winding of a transformer for the switching power supply and a ground, a rectification smoothing circuit (D0005, C0004, L0001, C0002) connected to a secondary winding side of the transformer for the switching power supply, an output voltage detection circuit configured to detect an output voltage value of the rectification smoothing circuit (D0005, C0004, L0001, C0002), a photocoupler configured to transmit the output voltage value to a control circuit that is configured to control the operation of the switching power supply, and a second switching element configured to receive a stop signal for stopping operation of the switching power supply, in order to provide for a transition from the low power standby state to the high-power state, characterized by the switching power supply further including: a photocoupler drive circuit (102, 104, 106, 110) configured such that when the second switching element has received the stop signal, in order to provide for a transition from the low power standby state to the high-power state, power output from an operating one of the low-frequency transformer power supply or the switching power supply is supplied to the photocoupler, and the stop signal for the switching power supply is transmitted to the control circuit via the photocoupler. a first switching element connected between a primary winding of a transformer for the switching power supply and a ground, a rectification smoothing circuit (D0005, C0004, L0001, C0002) connected to a secondary winding side of the transformer for the switching power supply, an output voltage detection circuit configured to detect an output voltage value of the rectification smoothing circuit (D0005, C0004, L0001, C0002), a photocoupler configured to transmit the output voltage value to a control circuit that is configured to control the operation of the switching power supply, and a second switching element configured to receive a stop signal for stopping operation of the switching power supply, in order to provide for a transition from the low power standby state to the high-power state, characterized by the switching power supply further including: a photocoupler drive circuit (102, 104, 106, 110) configured such that when the second switching element has received the stop signal, in order to provide for a transition from the low power standby state to the high-power state, power output from an operating one of the low-frequency transformer power supply or the switching power supply is supplied to the photocoupler, and the stop signal for the switching power supply is transmitted to the control circuit via the photocoupler. a photocoupler drive circuit (102, 104, 106, 110) configured such that when the second switching element has received the stop signal, in order to provide for a transition from the low power standby state to the high-power state, power output from an operating one of the low-frequency transformer power supply or the switching power supply is supplied to the photocoupler, and the stop signal for the switching power supply is transmitted to the control circuit via the photocoupler.