When using a Dell SuperSpeed USB 3.0 Docking Station (D3000), D1000, & D3100 USB 3.0 Docking Station with your laptop system you must use the AC power adapter attached to the system to charge the battery and power the system. If no AC adapter is connected to the system, then it runs off of battery power until exhausted and the system shuts down.
The AC power adapter for the Dock only provides power to the dock, not the attached system.
This is working within the design specification of the SuperSpeed USB 3.0 Docking Station (D3000), D1000, & D3100 USB 3.0 docks.
These docks were not designed to provide DC power to the system using the USB 3.0 connection to the system.