Abstract: A power supply device comprising a switch assemble, a voltage transformation circuit and a processor is disclosed. The switch assemble may include a first switch and a second switch connected with each other in parallel. After the first switch turns on, the voltage transformation circuit is electronically coupled to AC power and provides a DC voltage output for powering the processor to turn on initially. The first switch will turn off after the processor is powered up, and the powered processor operates to control the second switch to turn on so that the voltage transformation circuit is coupled to AC power through the second switch and provides DC voltage output for enabling the processor to continue to operate. The processor is further configured to control the second switch to turn off according to performances of a load coupled to the transformation circuit.