A measure took effect earlier in February that will affect virtually everyone in the United States. While it drew little public notice, it will cut your energy bill and reduce harmful pollution.

What was it? Eagerly awaited national energy efficiency standards for the little black boxes on the cords that connect many of our electronics — such as smartphones, computer laptops and electric toothbrushes — to wall outlets. Known as external power supplies, or the less elegant term “wall warts,” these power adapters may be small, but they consume a lot of energy.

With 5 to 10 external power supplies in the average U.S. household, the new efficiency standards are projected to save consumers $300 million a year in electricity costs and reduce the carbon pollution that fuels dangerous climate change.

The standards, which will make new external power supplies up to 33 percent more efficient, are an important step to achieving President Obama’s goal of reducing carbon pollution by at least 3 billion metric tons by 2030 through efficiency rules for appliances and federal buildings.

The U.S. Department of Energy (DOE) projects that the new standards for external power supplies alone will cut nearly 47 million metric tons of carbon dioxide over 30 years, equivalent to the annual electricity use of 6.5 million homes.

A little history

The Natural Resources Defense Council (NRDC) has long regarded power supplies as a hidden opportunity for significant energy savings. California, ever the environmental trendsetter, established the first efficiency standards for external power supplies in 2004 with NRDC’s help. In 2005, Energy Star also developed a standard, allowing manufacturers to attach the label signifying the most energy-efficient models. National mandatory external power supply energy efficiency standards were established in 2008.

Eight years later, updated federal standards took effect on February 10 after a lengthy public input process. The revised standards strengthen efficiency requirements and extend them to new types of power adapters not previously covered. This makes sure that the vast majority of these devices now use the best available technology to minimize energy wasted as heat. (Efficient power supplies are much cooler to touch, and much smaller in size, than their predecessors were 12 years ago, before the first standards went into effect).

Overall, big savings will result

According to an analysis by the Appliance Standards Awareness Project, which has worked with NRDC to promote energy efficiency, the typical household will realize savings of up to 30 kilowatt-hours a year once all adapters in the home comply with the new standards. This may not be huge savings per household, but nationally it adds up to 93 billion kilowatt hours over the next 30 years and 47 million metric tons of carbon dioxide pollution, equivalent to the annual emissions from nearly 10 million cars.

While few people give those little black adapters much thought, more than 1 billion are in use in the United States. And 340 million new external power supplies were sold in 2009, according to DOE’s analysis. But there were probably far more sold last year, given the rapid growth of the electronics market.

The power adapters convert power from an AC wall outlet to the lower DC voltages needed to charge laptop computers, smartphones, and other devices. External power supplies were a good candidate for efficiency standards because they draw power — so-called no-load power consumption — when plugged in, even if disconnected from a device such as a phone or connected to a fully charged device. This idle load contributes to the $19 billion a year Americans spend on “always-on” energy use by inactive appliances, electronics and miscellaneous electrical devices.

When connected to a device, the adapters also can be highly inefficient, sometimes dissipating half or more of the power they draw in the form of wasted heat.

While adapters consume a modest amount of energy individually, the drain on power adds up. As Senator Everett Dirksen once put it referring to federal spending: “A billion here, a billion there, and pretty soon you’re talking about real money.” Or in this case: A kilowatt here, a kilowatt there, and pretty soon you’re talking about large energy savings and substantial pollution reduction from big power plants.

Battery chargers will be next

Separately, NRDC is pressing DOE to finalize the first federal efficiency standards for the roughly 500 million battery chargers sold annually in the United States. Battery chargers include not just the external power supply, but also the battery itself and the charge control circuitry component of devices that use rechargeable batteries, such as smart phones and laptop computers. DOE last summer released updated proposed standards that are similar to the standards already in place in California and Oregon.

DOE originally considered establishing efficiency standards for battery chargers at the same time as external power supplies. But NRDC and other groups urged the agency to complete action on the external power supplies while work continued on the standards for battery chargers.

Making both external power supplies and battery chargers more efficient can lead to substantial savings to consumers’ pocketbooks and significant health and environmental benefits, not only because of the huge volume sold annually, but because the number is sure to grow, given the proliferation of electronic devices in our lives.

Pierre Delforge is director of high-tech sector energy efficiency for the NRDC in San Francisco. This post originally appeared at NRDC Switchboard.