This guy tested this, and found that chargers measure 0.0 watts. By plugging a bunch in simultaneously, he was able to get a nonzero reading, but still less th

This guy tested this, and found that chargers measure 0.0 watts. By plugging a bunch in simultaneously, he was able to get a nonzero reading, but still less than 0.5 watts: http://www.inference.phy.cam.ac.uk/sustainable/charger/ http://www.inference.phy.cam.ac.uk/sustainable/charger/ (He is now Chief Scientific Advisor to the Department of Energy and Climate Change in the UK.)