A power switch circuit includes a voltage selection unit, a first level shift circuit, a second level shift circuit, a first transistor, a second transistor, and a leakage control unit. The voltage selection unit outputs a greater one of a first variable voltage and a system voltage as an operation voltage. The first level shift circuit outputs a first control signal by shifting a voltage of a first input signal. The second level shift circuit outputs a second control signal by shifting a voltage of a second input signal. The first transistor outputs the first variable voltage according to the first control signal. The second transistor outputs the system voltage according to the second control signal. The leakage control unit establishes an electrical connection between first terminal of the first transistor and the control terminal of the second transistor according to the operation voltage.