Did you try a different usb cable or charger?
Most newer Motorola Android phones (including the Droid) accepts a standard micro USB connection. Use of a standard micro sub data cable works when charging off the PC.
As for USB charging adapters, Motorola phones that accept micro USB will not charge of most regular USB charge adapters. Those USB adapters rated for Motorola phones, Apple iPhones and sometimes some universal phone chargers will work.
You can also wire up a small adapter to trick Motorola android phones to charge from a regular USB adapter by connecting the 2 pin/ data - (usually a white wire) and pin 3 data + (usually green) http://pinouts.ru/Slots/USB_pinout.shtml
This will trick Motorola Android phones that they are on a legit charger and charge the battery. Make sure the 2 crossed wires are on the side going into the phone. Cutting and splicing a USB extension cord will do the trick if you do not feel like modifying an existing USB adapter.