A modular power distribution unit (PDU) for supplying electric power to attached equipment in environments such as data centers, computer rooms, and communication centers, where power requirements for attached equipment may vary. The power distribution unit includes a frame and one or more user-replaceable power modules, which fit into slots in the frame. Each power module provides one of more plug receptacles for attaching equipment to provide power thereto. The power modules are available in a variety of receptacle types, receptacle numbers, and power rating configurations to accommodate various equipment in a particular environment, as needed. The frame includes an internal connector panel for distributing power from a power source to the power modules when they are inserted in the frame. The power modules may be removed, installed, and interchanged in the frame without interrupting power to other power modules or to the power distribution unit.