The Energy Star program is one of the best known standards for helping consumers choose energy efficient products. It was first introduced by the United States Environmental Protection Agency in 1992, but has been since been adopted by Australia, Canada, Japan, New Zealand, Taiwan and the European Union as well.

The current Energy Star 4.0 computer specifications came into effect on July 20, 2007, and was notable for its requirements for power supplies that met the standards of the 80 PLUS program.

The efficiency of a computer power supply is measured by the amount of energy it supplies divided by the amount of energy that is drawn. A 500 watt power supply that is only 50% efficient would actually draw 1000 watts of power in order to supply the wattage needed, with the rest of the energy being converted into waste heat. This waste heat must be removed through the use of fans from the computer into the ambient air. Often, this air is also cooled through air conditioning, drawing even more power. 
 
Alternatively, an 80% efficient 500 watt power supply would draw 625 watts, with only 125 watts of wasted heat. The majority of computer systems draw less than 500 watts at full load, even with the latest video cards from NVIDIA and ATI.

This massive reduction in power consumption and waste heat is the driving principle behind the 80 PLUS program. Power Supply Units (PSUs) are typically most efficient between half and three quarters load. They are much less efficient at low load, and somewhat less efficient at maximum load. To qualify for an 80 PLUS sticker, a power supply must achieve at least 80% efficiency at three specified loads (20%, 50% and 100%) of the maximum rated power of the PSU.

Before 80 PLUS certification was introduced, most PSUs had 50% to 70% efficiency ratings. Most PSUs now meet the minimum standards of the 80 PLUS program, and it has become the market standard.

New tiers were therefore brought into effect in 2008 to highlight more efficient PSUs. The 80 PLUS Bronze level requires 85% efficiency at half load, and 82% efficiency at 20% and 100%. Silver and Gold levels were also introduced with higher efficiencies. Cooler Master was the first company to introduce a PSU at retail with 80 Plus Silver Certification, while OCZ Technology introduced its new Z-Series power supplies with 80 PLUS Gold and Silver certification recently. There are currently 132 PSUs certified at the 80 PLUS Silver level, while 88 PSUs are available at the 80 PLUS Gold level. 

The latest statistics from the 80 PLUS program show that there are now 1,610 PSUs that at least meet the basic 80 PLUS requirements. Since so many efficient power supplies are available to the public, new Energy Star requirements were created last year to raise the bar. Those requirements are now coming into effect.

The new Energy Star 5.0 specifications for computer require 80 PLUS Bronze level certified power supplies. There are 708 PSUs that have been certified to meet the 80 PLUS Bronze level or higher.

All computer products (except for game consoles) manufactured on or after July 1, 2009 must meet the Version 5.0 requirements in order to qualify for Energy Star certification. This includes models originally qualified under Energy Star 4.0 specifications.

Servers are not covered under these specs. Instead, the EPA released Version 1.0 of the Computer Server specifications on May 15, 2009. It covers standalone servers with one to four processor sockets. A second tier to the specification covering servers with more than four processor sockets, as well as blade servers and fault-tolerant machines is expected in late 2010. Data centers using these servers consume massive amounts of power, and even a small percentage increase in efficiency can yield millions in savings.

The full Energy Star 5.0 specifications for computers are available here.