You may have heard about new efficiency standards for external power supplies used by laptop computers, printers, cordless telephone systems, and a host of other electronics products. These power supplies, also known as AC/DC adapters, “bricks” or “wall warts,” transform AC power that comes from the electrical outlet to DC power that sensitive electronics can handle—and they can be quite inefficient. Until recently.

Newer external power supplies that meet the current, voluntary Energy Star requirements can achieve efficiency levels of up to 84 percent, as opposed to 20 percent to 60 percent efficiency in older power supplies. The higher efficiency levels will save you electricity, as more inefficient power supplies require more continuous power and dissipate the wasted energy as heat. More efficient power supplies also consume less energy when plugged into an outlet but are disconnected from the electronic device. (See “Why Your Electronics Suck [Energy]” for more on this.)

The issue of energy efficiency in power supplies seems mundane, but Energy Star estimates that 11 percent of the United States’ electric bill is represented by electricity flowing through power supplies. And the savings of using more efficient power supplies can be significant.

California has mandated higher efficiencies up to 85 percent in external power supplies of new products, starting in July 2008, and the recently passed Energy Independence and Security Act extends California’s mandate to the rest of the United States. Exempted are external power supplies also used as battery chargers like those for cell phones. The voluntary Energy Star program will raise the stakes even higher with a revised spec for external power supplies to go into effect later this year. We may see efficiency levels of 87 percent for products consuming 36 watts or more, though that can change, as the spec is not yet final.

So how can you tell if you have an efficient external power supply? Energy efficiency expert Chris Calwell, vice president of research and policy for Ecos Consulting tips us off to the International Efficiency Marking Protocol used to identify efficient power supplies. Newer power supplies may have a marking, usually found on one side amid a host of nearly illegible power ratings and logos. There, look for a small Roman numeral in a circle:

-If you have a III, that means the power supply meets current Energy Star levels and can be 84 percent efficient for laptop computers and other products that use more than 50 watts when being operated.

-A marking of IV means it meets the new California and Energy Act requirements of up to and more that 85 percent efficiency for laptops and the like. (There are separate, formula-based requirements for devices that use less power, such as some ink jet printers, answering machines, standalone battery chargers and cordless phones.)

-Roman numeral V will be used on external power supplies that meet Energy Star’s revised specification due later this year.

To see a chart of how to read the markings, go to Energy Star’s page on the International Efficiency Marking Protocol.

About the Author:
Steven Castle - Contributing Writer

Steven Castle is a writer, editor, and humorist who recently completed Filthy Rich Things, a savage satire on our thirst for success and wealth. He is presently expanding his magazine work by writing more about alternative energy sources and green building.