As said before, power supply units tend to lose some of its power to heat production. This results in less power put to good use compared to the power that is drawn from your socket. PSU certifications show you just how well your PSU should perform.
Power Supply Unit efficiency
There are several different kinds of certifications for PSU’s. The normal 80 PLUS certification means that a certain PSU efficiently uses 80% of the power consumed at 20% load, 50% load and 100% load. Every PSU loses power to heat and 80% efficiency is actually pretty good. There are of course power supplies that go over the 80% and those gain other certificates. In all there are 6 kinds of 80 PLUS PSU certifications to be had, where each they all indicate a certain degree of efficiency of the power supply unit.
PSU Certification standards
As you can see it goes up all the way to over 90% efficiency, which is pretty incredible, but is not that much of a necessity for the average consumer. Anything with an 80 PLUS certification or 80 PLUS bronze should do more than well for your computer and basically tells you that you are buying a decent PSU.
Besides efficiency there are of course more things to look at when buying a power supply unit. One of things is a modular design.