I use this from Newegg and it does come with a tip that works in the 770. Assume its the same for the N800
http://www.newegg.com/Product/Produc...82E16875999020.

BTW, anything charged from a USB port will take a long time since the amps on a USB port are far lower then the amps provided by the nokia charger. The device I mention above works much better as supplementary power then as a charger.