Abstract: A DC electrical power supply system for converting AC power to DC power for various telecommunications equipment loads includes plural rectifiers mounted on one or more shelves and adapted to be inserted on and removed from said shelves, at will. One or more voltage converters may be inserted and removed from said shelves at will and include adapter plates for supporting the converters in place of a rectifier unit. The power supply system includes a frame supporting the shelves and a cabinet which includes busworks for connecting the rectifiers to circuit breaker tiers and to a battery pack. Low voltage disconnect devices may be interposed in the buswork at selected locations to provide operation in a battery protection mode, load protection mode and load shedding mode. The circuit breaker tiers, buswork, shelving, rectifier units and converters are all accessible for connection and disconnection from the front side of the power supply system.