A power supply system includes a plurality of battery modules and a control unit, and supplies electric power from the battery modules in an uppermost stage and a lowermost stage to a load. The control unit is configured to perform ON/OFF control for setting the battery modules to an ON state in an active time, setting the battery modules to an OFF state in a non-active time, and alternately repeating the active time and the non-active time. The control unit is configured to delay an ON/OFF control timing for the battery module in a lower stage adjacent to the battery module in a higher stage by a control delay time in comparison with the battery module in the higher stage. The control unit is configured to randomly determine the control delay times for the battery modules in lower stages than the battery module in the uppermost stage.