Xbox360 powercord.
Ok, so you probably know it is fairly large. There are reasons for it.
John Porcaro has the reason for the increase in the size of the powercord.
Also, another MVP, Mike/Bobafett/Surly Duff has a comparison shot of the Mac Mini powercord, and the Xbox360 powercord.

Thanks Mike!
Ok, just thought of this. Now...this is not an actual power-cord. It is actually a power supply. So, think of that large box in your PC, and put that in the casing. That is what you have.