Originally Posted by Bremen Cole
While I agree with you, it is really not all that rare that a device has a USB sync/charge option, and a charge only AC adapter connection. And it does charge through USB, if it is plugged into a USB connection on an active computer. I never trust USB to charge a device. At best it is a trickle charge, and a real AC adapter gives a more constant current and quicker charging.
(I apologize if I am being redundant or misunderstood something)
The computer must be powered and the main memory mounted, if you unmount/safe remove, the device doesn't charge. Of course if the computer is suspended the device doesn't charge. At least with my prs700. My Imate charges from usb and doesn't need to be syncing and the computer can be in suspension mode. I think that it is something related with charging optimization, but Im not sure. Never tried an AC adapter. I have an AC/usb charger and a adaptor to a round tip (from an external HD), but never tried it.