Why are power supplies built into computers where they get hot and noisy, instead of being separate wall-warts like most other electronic appliances? Because computers have been designed to work with different voltages and you would need a big bundle of wires to carry the different supplies to your computer. Engineers at Google, tired of running tens of thousands of computers with inefficient power supplies, has proposed a new standard for "high efficiency power supplies for home computers and servers" based on everything running on 12 volts only. They say that it would save 40 billion kwh over three years, worth $5 Billion. Founder Larry Page complained about this in January: "I'm going to just plead with all of you, let's get the power supply problems fixed, or let's get all these devices talking together," he said during a keynote address. It would have significant implications in the way we wire houses if this caught on.
12 volt systems don't work for toasters or irons or anything that takes a lot of power, but now, with exception of the kitchen and the laundry, it works for everywhere else in the house, including lighting. A separate system of distribution for 12 volts would eliminate wall-warts; would reduce EMF; would be safer for kids. Read Douglas Adams on Declaring war on dongly things" and ::New York Times