A switch, a power conversion apparatus, and a power supply system. The power supply system includes a control unit, a switch, a direct current source, and a power conversion unit. The switch is electrically connected between the direct current source and the power conversion unit, and the control unit is configured to send a switch-off signal to the switch when a fault occurs on the direct current source or the power conversion unit. The switch includes a contact component, a trip-free structure, and a knob that are sequentially disposed in a stacked manner in a first direction. A trip unit of the trip-free structure is configured to receive the switch-off signal, to unlock the trip unit from the cradle. The cradle drives the connecting rod structure to move, to separate the moving contact from the fixed contact.