PC Power Supply Efficiency

How The Efficiency Rating of a Power Supply Can Save You Money

Seasonic SS-660XP2 Platinum Power Supply
Seasonic Platinum 660W PSU. ©Seasonic

Personal computers use a tremendous amount of power these days. As the processors and components get more powerful, so does the amount of energy they need to consume. Some desktop systems now can consume almost as much power as a microwave oven. The problem is that even though your PC may have a 500 Watt rated power supply, the amount of power that it actually pulls from the wall could be much higher than this.

This article takes a look at how much energy a power supply uses and what consumers can do when making a purchase to try and reduce that consumption.

Power In Versus Power Out

The electrical power that is supplied to your house runs at fairly high voltages. When you plug your computer system into the wall for power, this voltage does not flow directly to the components within the computer. The electrical circuits and chips run at much lower voltages than the current coming from the wall outlet. This is where the power supply comes in. It converts the 110 or 220-volt incoming power down to the 3.3, 5 and 12-volt levels for the various internal circuits. It needs to do this reliably and within tolerances. Otherwise, if can damage the components.

Changing the voltages from one level to another requires various circuits that will lose energy as it gets converted. This means that the amount of power in watts used by the power supply will be greater than a number of watts of energy that is supplied to the internal components.

This energy loss is generally transferred as heat to the power supply and is why most power supplies contain various fans to cool the components. This means that if your computer uses 300 Watts of power on the inside, it is using more power from the wall outlet. The question is, how much more?

The efficiency rating of a power supply determines how much energy is actually converted over when it converts the wall outlet power to the internal power components.

For example, a 75% efficiency power supply that generates 300W of internal power would draw roughly 400W of power from the wall. The important thing to note about a power supply is that the efficiency rate will vary depending upon the load amount on the circuits as well as the condition of the of the circuits.

ENERGY STAR, 80Plus and Power Supplies

The ENERGY STAR program was originally established by the EPA as a voluntary labeling program designed to indicate energy efficient products. It was initially established for computer products to help corporations and individuals mitigate energy expenditures. A lot has changed in the computer market since the program was initially established back in 1992.

Early ENERGY STAR products did not have to meet very strict energy efficiency levels because they did not use as much power as they do now. Because of these increasing levels of power consumption, the ENERGY STAR program has been modified multiple times. In order for new power supplies and PCs to meet the ENERGY STAR requirements, they must meet an 85% efficiency rating across all rated power output. This means that if the computer is running at 1%, 100% or any level in between, the power supply must reach a minimum 85% efficiency rating in order to get the label.

When looking for a power supply, look for one that carries an 80 PLUS logo on it. This means that the power supply efficiency has been tested and approved to meet the ENERGY STAR GUIDELINES. The 80 PLUS Program provides a list of power supplies that have to meet the requirements. There are seven different levels of certification. They range from least to most efficient with 80 Plus, 80 Plus Bronze, 80 Plus Silver, 80 Plus Gold, 80 Plus Platinum and 80 Plus Titanium. To meet the ENERGY STAR requirements, you need to get at least an 80 Plus Silver rated power supply. This list is updated periodically and provides downloads of PDF's with their test results to let you see exactly how efficient they were.