A power distribution unit (PDU) having a connector to connect to an input power supply and a plurality of power outlet sockets for receiving plugs having a number of pins. Each power outlet socket has a mechanical locking mechanism movable between a locked position and an unlocked position when a plug is inserted into the power outlet socket to lock and unlock a plug pin in the power outlet socket. Absent actuation the locked position is adopted. Each power outlet socket includes an externally, manually actuatable, first release element, and an internally, electrically actuatable, second release element. A power sensor detects whether or not power is being drawn and, for power outlet sockets which currently host a plug and are not drawing power, the second release element is actuated by the PDU so as to unlock the mechanical locking mechanism, thereby freeing up the associated plugs for removal.