A testing system for a power supply (40) includes a testing chamber (10), a control switch, an electrical load (50), an AC source (60), and a PLC (30). The power supply has a voltage choice switch. The testing chamber receives the power supply therein. The testing chamber provides a first or a second ambient temperature and supplies a testing environment for the power supply. The control switch switches the power supply to operate between a standby state and an operational state. The electrical load is connected to the power supply. The AC source is connected to the power supply. The AC source outputs the first voltage or the second voltage to the power supply. The PLC controls switching states of the voltage choice switch and the control switch in a manner such that the power supply selectively operates in one of combined switching states of the voltage choice switch and the control switch.