Abstract: During switching over of AC power supply, the single-source single-charging DC power supply system needs battery to supply power for DC loads for a short period, and the failure of switching over or the fault of battery would affect the normal operation of secondary load equipment, which is of low reliability. By modifying the wiring mode of original DC power supply system and providing standby charging module, it is ensured that DC system would still supply power reliably in case of partial AC failure or the fault maintenanie of AC switching device. The tests and onsite inspections prove the effectiveness of such a scheme.