3740QM on E6430 frozen on 800MHz with <90W adapterc

The title of the thread is meant to be fully self-explaining. I can't understand one very unexpected thing:

E6430 showed as very powerful  model with high performance sustained over long time. Even on battery. (for example I saw 51W from cpu + 25W approx(NVS5200 has not wattcounter) for GPU = TOTAL about 75W on battery)

So the performance is unlimited, when running ON BATTERY or WHEN >=90W AC adapter ("power supply" in English).

But when I plug 45 OR 65W adapter  why is the CPU frequency FROZEN  on just 800MHz ?? When doest this happetn even if the battery is fully charged? 

It cannot even be changed in throttlestop...

PS: i know that these adapters are underrated for E6430, dialog box  with that information appears. The point of the question is that the presence of power supply is supposed to at least leave the system performance on the same level as running on battery.