DSP Design created a PC that gets its power through an Ethernet cable. This could be interesting as a universal power supply for a lot of low-power computer hardware. Ethernet cables are the same in each and every country while power sockets and plugs differ by country.
Power-over-Ethernet (PoE) works because when data is sent down network cables it is represented by voltages. Some PoE equipment uses spare wires in cables that link computers back to network hubs and pump power down these. Others pump power down the same lines as the data traffic. The current PoE specifications have an upper limit of 15.4 watts.
Soon the Power Over Ethernet Plus specification will be released - this will increase the maximum wattage from 15.4 watts to 30-35 watts. More details at BBC