When a power conversion unit is in a working mode, the power conversion unit converts an alternating current power from an alternating current power supply apparatus into a direct current power. Then, the power conversion unit sends a power starting signal to a first switch control unit. After the first switch control unit receives the power starting signal, the first switch control unit turns on a first switch unit, so that an overall capacitor impedance formed by a first capacitor and a second capacitor is smaller than a first capacitor impedance formed by the first capacitor. When the power conversion unit is not in the working mode, the first switch control unit turns off the first switch unit, so that the overall capacitor impedance is equal to the first capacitor impedance.