Green Plug wants to rewire your gizmos and even your home, and ditch most of your “wall wart” chargers in the process. Instead of each gadget having its own charger built to deliver just the right amount of power, it would have a chip that tells a universal charger how much power it needs.

At this week’s DEMO conference in California, sample devices from Green Plug ran off USB cables that can carry data as well as power, and they plugged into a transformer that looked more like a USB hub. Along with saving space, the technology could save some electricity. When the battery of a Green Plug device is full, it tells the charger not to send it any more juice. (Nokia is using similar technology on some of its cellphones.) Plus, fewer wall warts means fewer wasted watts. Even the smallest, most efficient transformers draw at least 0.3 watts just by being plugged in. If you replace, say, three chargers with one Green Plug hub, you’ve cut the waste by two-thirds.

While the Green Plug folks talked about saving a lot of power, they weren’t so good at putting numbers behind their claims. One example they did provide was pretty modest: The average ($100,000) house has about 30 wall warts. Ditching most of them in favor of Green Plug chargers could save $20-$30 in electricity bills annually. Good, but not quite saving the world–or your budget.

Of course, it could go further. The Green Pluggers said you could wire an entire building with the technology. So a house might have just one charger in the basement, and every outlet would be a smart power connector. Of course, then every electronic device in the house would have to be equally smart.

Anyway, they will be starting out more modestly. Green Plug expects to ship its first chips towards the end of the year, and consumer gadgets may appear sometime in 2009. It claims to have signed on at least one big company that sells chargers in big-box stores like Best Buy, but didn’t name names.