PoE is a technology to deliver voltage (and data) over a standard twisted pair cable in an Ethernet network. This technique is used to provide network equipment (think of webcams, switches, VoIP phones, etc.) with power. There is a limited power to a network cable, so for large consumers as a computer or server, PoE is not suitable. Read More
PSU comes from the computer world and is there the abbreviation for Power Supply Unit. So it is the power supply of a computer system. It converts the 220v mains voltage into the 12, 5 or 3 volt voltages with which the computer parts work. The power supply is connected to the main board, the hard drive, the DVD drives, video card, processor, ect. External devices (monitor, printer, scanner, etc.) usually do not receive power from the power supply, but they need power through a power outlet. Also soldiers use the abbreviation PSU, in that case one is about a personal standard equipment.