What Do PSU Efficiency Ratings Actually Mean?

When determining an appropriate PSU to use for a configuration, we all know to look to the Power Supply Efficiency Rating, but what exactly is the Power Supply Efficiency Rating telling us? Is an 80 Plus Gold rated PSU really that much better than an 80 Plus Bronze rated PSU? And what does 80% efficiency even mean? These are all very common questions and the answer isn’t quite as obvious as it may seem.

Let’s start with basics…

When your system is on and using energy, the PSU is taking AC power from the outlet and converting it to DC power for the components to use. The PSU will typically be drawing more energy than it needs. For example, if the components are calling for 250W, the PSU could be taking anywhere from 272W to 416W… depending on the efficiency rating. It is also important to note that even if you have a 500W PSU, that does not mean you will be taking 500W. The amount of energy drawn is based on what your components need to run. There is a general misconception that if, for example, you have an 80% efficient 500W PSU, it will only be able to supply 400W’s to your system. That is incorrect. For the sake of explaining, we will use a 500W PSU in a system that only requires 250W’s of power (50% load) to run. If you have an 80% efficient PSU, it will draw 312.5W of power to your system. If you have a have a 90% efficiency rated PSU, it will only draw 278W. The extra power being drawn is just turned into waste, which can be very harmful to your system. That will be explained shortly.

80 PLUS Bronze vs 80 PLUS Gold vs 80 PLUS Platinum

The 80 PLUS efficiency rating system tests PSU’s based on a 20%, 50% and 100% load. Meaning using 20% of the total PSU’s maximum watt usage (20w out of a 100w PSU). Below are the rankings:

	20% Load	50% Load	100% Load
80 PLUS	80%	80%	80%
80 PLUS Bronze	82%	85%	82%
80 PLUS Silver	85%	88%	85%
80 PLUS Gold	87%	90%	87%
80 PLUS Platinum	90%	92%	89%

 

Why does this matter to you?

Well it’s actually very important. The extra power being pulled by the PSU is waste energy, which can result in a few downfalls over your system. First, this power can be excreted as heat. Obviously, that can be trouble for your system. The waste can also be given off as field waste, which can be harmful to the other components in your computer. These waves can very easily cause damage to your GPU or motherboard.