The Axim series takes a LOT of power to charge, particularly from a really dead battery. The Dell power supply is rated at 2A, or 2000mA. The standard USB port only provides 500 mA. If you wall charger is not rated at 2000mA for output, then it will struggle to charge a dead battery. Read the first couple of pages of
this thread for some details of the power demands of the X50 and X51 series.