Hi. I think I may have a problem with my USB adaptor? It is a two pin adaptor mated with a 3 pin British plug, fitted with a 3 amp fuse. When I charge my tablet it only charges for a while and then stops. The adaptor feels quite warm but no more so than my mobile phone adaptor. It does work but only for a while. Under these circumstances would ACER possibly send me a new charger? Also this may seem a silly question but can this unit be charged when turned off? If so, mine does not. (unless it's the adaptor again?) Any answers/help would be gratefully recieved. Thank you.