I see, internal batteries operate at one voltage, the AC input operates at a different voltage, so going in the ac port with a power back will require 19 volts for it to work with out the internal battery? correct?
Observe that the internal battery voltage stated is the _nominal_ battery voltage. At the end of a charge cycle the voltage on the internal rechargeable battery will be significantly higher than the nominal value.
In addition, the laptop needs a few additional volts on the external supply to overcome cable losses, reverse voltage protection devices, fuses, charge current measuring devices, voltage monitoring devices etc.
All this to secure a rapid charging of the internal battery.
I.e, just what a given "19 Volts" laptop is willing to provide of useful services when fed a meager 12 VDC on the external power port, I somehow doubt can be inferred from the technical spec sheet alone :-).
Jon