A power supply system, comprising: a power converter (100, 100a) and a switch mechanism, each phase of three phases of an output end of the power converter (100, 100a) is configured to be connected to a downstream circuit being an alternating current power network by using the switch mechanism, the power converter (100, 100a) is configured to perform electric energy conversion, and the switch mechanism comprises a first switch component (K1, K3, K5) and a second switch component (K2, K4, K6) in each phase that are connected in series; the power supply system further comprises: a controller; a first passive component and a second passive component; a first capacitor configured to be connected with its first end to a neutral point N of the alternating current power network; a first bus connection line (Bus+) and a second bus connection line (Bus-) connected to an input end of the power converter (100, 100a); a second capacitor and a third capacitor configured to be connected in series between the first bus connection line (Bus+) and the second bus connection line (Bus-), and a common point of the second capacitor and the third capacitor is a direct current bus midpoint (BUS_N), the second capacitor and the third capacitor equally dividing a direct current bus voltage; a grounded class Y-capacitor consisting of a fourth, a fifth and a sixth capacitor each connected to a second end of the first capacitor, wherein the fourth capacitor is connected to the first bus connection line (Bus+), the fifth capacitor is connected to the second bus connection line (Bus-) and the sixth capacitor is connected to the direct current bus midpoint (Bus_N); wherein two ends of the first switch component in only one phase (K1, K3, K5) of the output end of the power converter (100, 100a) are connected in parallel to the first passive component, and two ends of the second switch component in only one phase (K2, K4, K6) of the output end of the power converter (100, 100a) are connected in parallel to the second passive component; and the controller is configured to: control the second switch components of all phases (K2, K4, K6) to be turned on, and when a voltage difference between the two ends of the first switch component in the one phase is less than a preset voltage, control the first switch components of all phases (K1, K3, K5) to be turned on; or, control the first switch components of all phases (K1, K3, K5) to be turned on, and when a voltage difference between the two ends of the second switch component in the one phase is less than a preset voltage, control the second switch components of all phases (K2, K4, K6) to be turned on. a controller; a first passive component and a second passive component; a first capacitor configured to be connected with its first end to a neutral point N of the alternating current power network; a first bus connection line (Bus+) and a second bus connection line (Bus-) connected to an input end of the power converter (100, 100a); a second capacitor and a third capacitor configured to be connected in series between the first bus connection line (Bus+) and the second bus connection line (Bus-), and a common point of the second capacitor and the third capacitor is a direct current bus midpoint (BUS_N), the second capacitor and the third capacitor equally dividing a direct current bus voltage; a grounded class Y-capacitor consisting of a fourth, a fifth and a sixth capacitor each connected to a second end of the first capacitor, wherein the fourth capacitor is connected to the first bus connection line (Bus+), the fifth capacitor is connected to the second bus connection line (Bus-) and the sixth capacitor is connected to the direct current bus midpoint (Bus_N); wherein two ends of the first switch component in only one phase (K1, K3, K5) of the output end of the power converter (100, 100a) are connected in parallel to the first passive component, and two ends of the second switch component in only one phase (K2, K4, K6) of the output end of the power converter (100, 100a) are connected in parallel to the second passive component; and the controller is configured to: control the second switch components of all phases (K2, K4, K6) to be turned on, and when a voltage difference between the two ends of the first switch component in the one phase is less than a preset voltage, control the first switch components of all phases (K1, K3, K5) to be turned on; or, control the first switch components of all phases (K1, K3, K5) to be turned on, and when a voltage difference between the two ends of the second switch component in the one phase is less than a preset voltage, control the second switch components of all phases (K2, K4, K6) to be turned on.