A power supply apparatus including a multi-outputs power supply circuit and a first regulating circuit is provided. The multi-outputs power supply circuit has a plurality of output terminals. The multi-outputs power supply circuit provides a first voltage from one output terminal among the output terminals and provides a second voltage from another one output terminal among the output terminals, where a rated voltage value of the first voltage is greater than a rated voltage value of the second voltage. The first regulating circuit is coupled between the one output terminal and the another one output terminal, where the first regulating circuit is enabled when the first voltage exceeds a first threshold, and begins to regulate the second voltage after being enabled.