Until recently the power adaptors were made using copper wires. About half the power they drew from the wall, and sometimes as much as 80 percent would be lost in conversion. As a result, electricity bills and carbon emissions were both higher that necessary. Making the conversion of high-voltage alternating current to low-voltage direct current using integrated circuits is much more efficient, with as little as 20 percent of the power being lost. The technology, although available for several years, cost around 30 percent more making it less attractive for manufacturers to switch. Further, power adaptors cost very less (about $2 or less) and most the production contracts to manufacturers in Taiwan and China were negotiated and determined on the basis of the manufacturer's ability to reduce the selling price by a few cents a piece. Consumers also do not give as much attention to power adaptors in their phone or laptop purchase decisions. All these factors limited manufacturers' incentives to switch to energy efficient technologies.
Around seven years ago, the Natural Resources Defense Council and Ecos Consulting, an energy consultancy, got manufacturers, power utilities and the state and federal governments together to talk about shifting to integrated circuits. It took two years to get regulations in place in America. With the biggest market adopting to the new technology, integrated circuit adaptors spread swiftly everywhere. For consumers the switch has meant lower power bills and smaller, lighter power adaptors. For the world as a whole it has meant a drop in global power consumption worth around $ 2 billion a years - saving $13 million tonnes of carbon dioxide annually worldwide, the equivalent of closing down eight coal-fired power stations.
Source: Vampires on a diet: How a boring gadget saved $2 billion-worth electricity. The Economist, A Special Report on the Carbon Economy, December 5th 2009