A redundant power supply system providing alternate standby includes at least one primary power supply, at least one secondary power supply and a power integration panel. Each primary power supply receives a first power ON/OFF signal and starts to output a primary duty power. Each secondary power supply receives a second power ON/OFF signal and starts to output a secondary duty power. The power integration panel is electrically connected to the primary power supply and the secondary power supply and has a standby mode to receive a power ON/OFF signal from a motherboard and output alternately at a selected time interval the first power ON/OFF signal to the primary power supply or the second power ON/OFF signal to the secondary power supply to make the primary power supply and the secondary power supply on standby alternately.