Power supplies are not sexy hence they are an often overlooked aspect of a computer's internal specifications.
This article advocates buying a PSU by weight! Joking aside it is a very interesting article and I have personally experienced a problem upgrading a machine and experiencing some weird problems which were caused, it transpired, by the PSU being unable to cope with the marginally increased power requirements. It was a PC from a now bankrupt PC supplier and the power supply was literally able to power the PC with almost no excess capacity!