A power supply with synchronized clocks includes a transformer for transforming an AC input voltage into a DC input voltage, a delay unit for delaying phase of a standard clock signal to generate a plurality of synchronization clock signals, a major DC-DC converter for adjusting voltage level and phase of the DC input voltage according to one of the plurality of synchronization clock signals to generate a major output voltage, and a plurality of parallel DC-DC converters each for adjusting voltage level and phase of the major output voltage according to one of the plurality of synchronization clock signals to generate a minor output voltage.