In addition to being unsightly, those boxy power adapters that come with almost all your electronics have an ugly effect on your electric bill. But that’s about to change under new federal energy-efficiency standards that quietly went into effect recently. The new standards require external power supplies to be 33 percent more efficient. And with 5 to 10 power adapters in the average U.S. home, the savings can add up quickly. (Learn how to tame the energy hogs in your home.)

External power supplies convert the power from a wall outlet into the lower voltages needed to charge laptops, smartphones, and countless other devices. They were considered a prime candidate for an efficiency upgrade because, when plugged in, they draw power all the time even if the devices they are charging are at full power, according to Pierre Delforge, the director of the High Tech Sector Energy Efficiency for the Natural Resources Defense Council. In older power adapters, much of that energy is wasted as heat.

More than a billion power adapters are in use in the U.S., and with the proliferation of electronic devices, that number is certain to grow. In addition to the wasted energy, a lot of money is being needlessly spent on these “always on” power adapters.

Starting February 10, almost all types of power adapters must meet the new standards, which means that any new smartphone, laptop, or other device manufactured after that date will come with the new energy-efficient external power supply. To experience the difference, touch the adapter when it’s plugged in: Newer ones should be cooler to the touch, while an adapter for an older device will likely give off some heat.

To save energy even with an older adapter, make sure you unplug it from the wall and your device once it's fully charged. The external power supply continues to draw power even when it isn’t connected to your device but is still plugged into the outlet.