A new type of charger called the Green Plug aims to replace the pile of power bricks under your desk with a hub that powers multiple devices at once, but only when they need it. The idea behind the system, due out early next year, is that software in gadgets would let them tell the hub exactly how much power they need. When its battery is full, the device tells the Green Plug to cut the juice. Current chargers keep drawing a small amount of power as long as they’re plugged into an outlet.