The instant disclosure provides a power supply system and control method thereof. The power supply system comprises at least two power supplies electrically coupled in parallel. The control unit of the power supply generates a wake-up signal or a sleep signal according to the loading status. A second communication port of each power supply is coupled to a first communication port of the next stage power supply to establish cascading communications architecture. The first communication port receives a wake-up signal from the second communication port of the previous stage power supply and outputs a sleep signal to the second communication port of the previous stage power supply. The second communication port receives the sleep signal from the first communication port of the next stage power supply and outputs the wake-up signal to the first communication port of the next stage power supply.