A short while back we did an article on external power supplies, those clunky AC/DC adapters that we use for laptop computers, cordless phones, printers and so forth. Most that are a few years old are terribly inefficient and waste electricity, especially if you leave them plugged in to an electrical outlet but disconnected from your electronic device. But new ones that come with products today can be quite efficient—up to 85 percent efficient, which is pretty darned good, considering old ones can be anywhere from 20 percent to 60 percent efficient. 

Newer, more efficient power supplied are often marked by a small Roman numeral of III or IV on a side of the adapter, beneath an array logos and specs. III means it meets current Energy Star requirements, IV meets California and new federal standards that go into effect in July, and V is reserved for a new Energy Star spec due to take effect later this year. These marks are called the International Efficiency Marking Protocol.

What can you do if you have an old, inefficient power supply, but which works with an electronic device you’d rather not dump? You can replace the old power supply with an efficient new one, says energy efficiency expert Chris Calwell of Ecos Consulting. “The [electronics device] doesn’t care how efficient the technology is that is providing low-voltage DC.” Though swapping external power supplies may be tricky. You’ll have to do some research and enter the confusing world of power supply specs. 

According to Calwell, a new power supply needs to meet three conditions to be used with an existing piece of equipment:

• Same output voltage as the old power supply (marked in volts).
• A maximum output current equal to or greater than the old power supply (marked in amps).
• An identical plug, in shape, size, and polarity. Shape and size are easy to verify, based on whether it fits in the socket of the device being powered.  Polarity is often indicated on the housing of the power supply, and mainly concerns whether the ground is on the jacket surrounding the plug or on the inside of the plug. There’s usually a polarity diagram, with a plus sign (+ for positive) and a minus sign (- for negative) that shows if it’s center positive or center negative. Look to match the diagram on your old adapter with a new one.

For a list of efficient external power supplies and they’re efficiency ratings, you can go to the Energy Star site and by family or by the end-use product. Not all the information you need is there, but it will give you an idea of the manufacturers who make adapters to suit your power output requirements. The manufacturers’ web sites aren’t very good at providing the info for things like the polarity, either. But a call or email to the company may help.

If you can shop for these in a retail store, all the better, says Calwell.

We wish it were easier. Ah, maybe someday. I’ve only started my search for an efficient adapter for a six-year-old laptop. It may well turn into a quest. 

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.