I have been chasing this problem for over a month. I have a 1.0 amp usb charger in my bedroom that I have used since I got the Thunderbolt in April, Worked fine. Recently the phone will not charge with this charger. Tried an iPad charger, also 1.0 amps. No good. Different cables, no change. Downloaded Battery Monitor Widget and found that when the original TB charger is connected, Battery Monitor shows "AC plugged" (and charges correctly). Any other charger, regardless of capacity, is only recognized as "USB plugged" and the phone actually discharges even though it is plugged in. I now realize that this occurred with the Gingerbread update. Not sure if it was the original update or the December update.
Has anyone else noticed this?