information about the active GPU in an APU system

When you connect it to a power source it automatically shifts things.
Also, to manually control which video card to be used, you can open CCC (Right click on desktop) go to switchable graphics and fiddle around with settings.

They let you choose which card to be used for which software or game.

Other than that you can do benchmarks (Kombuster) with laptop charger on and off to see the difference. ^^