External power supplies (EPS), also known as power adapters, are the small black boxes on the cord of many small or portable electronic devices such as laptop computers, tablets, modems, computer speakers, and cordless and cell phones. Power supplies convert household electric current (around 120 volts in the United States) to lower AC or DC voltages on which many electronic products operate.
The Energy Independence and Security Act (EISA) of 2007 established standards for single-voltage EPSs with output power ≤250 W, which took effect in 2008. In February 2014, DOE published a final rule strengthening the efficiency requirements for single-voltage EPSs and expanding coverage to other EPS types such as multiple-voltage, high-power, and medical EPSs, and EPSs for motorized applications and detachable battery packs. The new standards took effect in February 2016 and include minimum efficiency requirements for active mode and maximum power limits in no-load mode. Compared to the EISA standards, the current standards represent energy savings of 30-85%.
A 2016 rulemaking codified provisions of 2014 legislation that exempted certain service or spare part EPSs from efficiency standards.
According to DOE, annual shipments of EPSs are about 345 million, with the current standards affecting about 75-80% of those sales. Technology options for improving the efficiency of EPSs include improved transformers, low-power integrated circuits, and low-loss transistors.