The present invention discloses a power supply device with low standby loss. The power supply device comprises a main power converter and an auxiliary power converter. The main power converter comprises a bulk capacitor. The main power converter connects parallelly with the auxiliary power converter. When the power supply device is in a standby mode, the main converter is turned off and the auxiliary converter provides the output to the outputting load and the bulk capacitor. Moreover, when the power supply device is in a normal mode, the main converter and the auxiliary converter together provide the output to an outputting load. Under a normal mode, the main converter provides most of the power and the auxiliary converter operates in a power-limited finite value such that the topology of the power supply device achieves a low standby loss.