You may not think much about power supplies — those power cords with a bricklike appendage that converts AC power into the DC needed by cellphones, laptops and a host of other devices.

But touch that brick while any of those devices is on and it will probably feel warm. That's the energy lost during the conversion process. The power supplies hidden within desktop computers, TVs, cable boxes and other appliances also waste energy.

AC power supplies can waste $20 to $50 of what you spend annually on electricity. Nationwide, power supplies waste more than 58 billion kilowatt-hours yearly, equal to the annual output of 10 large power plants. That extra energy output translates into 40 million tons of the greenhouse gas carbon dioxide released into the atmosphere each year, according to Ecos Consulting, an environmental consulting firm.

A major culprit is the type of adapter known as a linear power supply, or transformer, which typically has an energy-efficiency rating of 30 percent to 60 percent. That means it loses 40 percent to 70 percent of the energy converted to DC when powering an appliance. A transformer can consume 2 to 5 watts just by being plugged in. Manufacturers like them because they're inexpensive to make.

More-efficient designs, called switching power supplies, can offer up to 90 percent efficiency. They use far less power, even when not powering an appliance. Trouble is, they also cost slightly more to produce than transformers.

As of Jan. 1, the Environmental Protection Agency (EPA) is expanding its Energy Star program to include external power supplies. Initially, to qualify for the seal, a power supply's average efficiency must fall in the top 25 percent of units on the market.

Energy Star-rated external power supplies should start reaching consumers during the first half of 2005. The Energy Star logo will be on the product box, but not on the power pack itself. Although most power supplies in use are internal, the Energy Star program won't cover those until at least the end of 2006 because they're more complex, according to the EPA.

Some devices not now rated, such as cordless screwdrivers and handheld vacuums, also won't be rated before 2006: Members of the Association of Home Appliance Manufacturers, which produce them, have yet to join Energy Star because, the association says, such testing isn't yet appropriate for those products. But come Jan. 1, 2006, manufacturers might have little choice about complying with new energy rules. That's when California deploys compulsory new standards in line with Energy Star. The mandates might have a powerful effect on industry compliance nationwide, since few companies will want to be excluded from the sizable California market.

Meanwhile, here are some steps you can take to be energy smart:

• Unplug the power supplies or chargers of products used infrequently or seasonally, such as those for a cordless drill or weed trimmer.

• Consider consolidating your power supplies on a single power strip with an on/off switch so that you can easily cut the current when you're not using or charging any devices.

• Before leaving for vacation, unplug TVs, cable boxes, PCs and other appliances you won't be using.

If you're replacing linear adapters with Energy Star-labeled switching supplies, make sure the voltage and current (amps) output of the new unit match that of your old one. This information should be clearly visible on the packaging and the unit itself.

You can learn more about using power supplies efficiently by going to www.efficientpowersupplies.org.

Copyright 2004, Consumers Union