a power sub - frame is provided for a system unit . the power sub - frame has four walls defining first , second , third and fourth sides of a open , rectangular frame . a fifth side is open for receiving a plurality of power supply units for powering the system unit . a power distribution board located at a sixth side of the frame opposite to the open side , for making electrical contact to the power supply units . the power sub - frame can be manufactured as a sub - assembly for the system unit , facilitating manufacture , testing and maintenance . the power sub - frame can be pre - assembled with power distribution logic and cabling ready to be mounted in a system unit . the system unit can , for example , be a computer system unit for rack mounting in a telecommunications application .