This is a little off topic but I would also like to charge my 770 and n800 off of a USB but I am looking for a different solution. I would like an adapter that plugs into my mini-USB that converts the plug into the power plug, I have seen things like this for pocket pc's, I have looked but can't make heads or tails of what exactly to search for. Like this
I found this but I am looking for something that is not so much and fits over the standard data cable for my tablet