How PC Power Supply Efficiency Can Reduce Electricity Costs

The efficiency rating of your power supply can save you money

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If your PC has a power supply rated at 500 watts, the amount of power that it actually pulls from the wall could be much higher. Learn how PC power supply efficiency affects electricity costs and how to reduce your energy bill with Energy Star products.

Information in this article applies broadly to a wide range of devices. Check the specifications of individual products before making a purchase.

What Is PC Power Supply Efficiency?

The efficiency rating of a power supply determines how much energy is actually converted from 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.

When you plug your computer into the wall, the 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. Therefore, the power supply must convert the incoming 110 or 220-volts to 3.3, 5, and 12-volt levels for the various internal circuits. The power supply must do this reliably and within certain tolerances to avoid damaging the device.

Changing the voltages requires various circuits that lose energy as it gets converted. This energy loss is generally transferred as heat to the power supply, which is why most power supplies have fans to cool the components.

How PC Power Supply Efficiency Affects Electricity Costs

The exact efficiency rate will vary depending on the load amount and the condition of the circuits. That said, a higher efficiency rating means that less energy goes to waste, which can have an impact on your power bill. Fortunately, it's easy to identify energy-efficient PC power supplies.

Energy Star and 80Plus Power Supplies

The Energy Star program was established by the EPA in 1992 as a voluntary labeling program designed to indicate energy-efficient products. It was initially created for computer products to help corporations and individuals mitigate energy expenditures.

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. In order for new power supplies and PCs to meet the Energy Star requirements, they must achieve an 85% efficiency rating across all rated power output.

When shopping for a power supply, look for one that carries an 80 Plus logo on it, which indicates an efficiency of 80% or higher. The 80 Plus Program provides a list of power supplies that have to meet the requirements.

This list is updated periodically and provides downloadable PDF files with test results so that you can see exactly how efficient a product is. There are seven different levels of certification ranging from least to most efficient: 80 Plus, 80 Plus Bronze, 80 Plus Silver, 80 Plus Gold, 80 Plus Platinum, and 80 Plus Titanium. To meet the Energy Star requirements, a product needs an 80 Plus Silver rated power supply.