I have to say I think you've been unlucky here. Mine has charged via the mains charger, a usb cable (from PC, from Playstation 2 and from a powered USB hub with no data connection). I have also given the phone a charge from an AA battery pocket charger which all worked fine...

The manual did state that charging by USB may not provide enough power if the phone is under heavy load at the time, but I've not even noticed that as an issue. I think perhaps you should swap it or get your phone looked at by a Nokia service centre.