A power supply apparatus (10) suppressing a transient voltage is applied to an input voltage (50). The power supply apparatus (10) includes a power supply circuit (20), a feedback signal generation circuit (30) and a feedback signal control circuit (40). If the power supply circuit (20) stops receiving the input voltage (50), the feedback signal control circuit (40) controls the feedback signal generation circuit (30) to discharge so that the feedback signal generation circuit (30) controls the power supply circuit (20) to decrease an output voltage (60), so that when the power supply circuit (20) receives the input voltage (50) again, the power supply circuit (20) avoids generating an output overvoltage condition for the output voltage (60).