A power supply failover system/method providing uninterruptable power to protected load devices (PLD) is disclosed. The system includes a failover switch controller (FSC) with inputs from an AC I/V monitor (AIV), AC cycle counter (ACC), failover switch timer (FST), and overcurrent protection timer (OPT). The FSC utilizes these inputs to control failsafe switching of a bypass phase switch (BPS) and AC phase switch (ACS) to the PLD when power from the APS is determined to be good by the AIV. When power from the APS is determined to be compromised by the AIV, the FPS disables the ACS/BPS and enables a DC switch (DCS) and battery isolation switch (BIS) to connect a DC source to the PLD after a time period determined by the FST. APS/DCS overcurrent protection is limited by OPT intervals allowing a smooth transition between the APS to DCS during power failover/failback.