All you need is a good wall wart
I have been using just a cheap wall wart to charge my Zen X-Fi. I have built a nice external battery pack/charger so that I can use it for much longer but I have just a cheap wall wart which works fine. The basic problem that most folks run into is that it charges at 500mAh unless you put some resistors on the d+/d- lines to trick the player into thinking it is plugged into a PC, that way it will charge at 1100 mAh.
If you are handy or you can find one there is a thing called a mintyboost 3 which can be adapted, add one PIC circuit to the output of the charge and it becomes a very stable power supply battery charger.