power adapter is defective
The power throttling problem you are having has nothing to do with the power adapter.
To try and fix the GPU POWER throttling problem, exit ThrottleStop and add this line to the ThrottleStop.INI file.
IGPU=100
This will set and lock the Intel GPU power limit to 100W. This should be more than enough to prevent this type of throttling.
CORE POWER throttling can usually be controlled by adjusting the PP0 Power Limit near the bottom of the TPL window. Many 4th Gen laptops locked the PL1 and PL2 power limits to their default values, 47W and 58W. If the PP0 Power Limit is not locked by the BIOS, check this option in ThrottleStop and set this to 58W. There should be no need to check the Lock option on the right side of the PP0 Power setting. Do some testing first. You can leave the PP0 Turbo Time Limit at the minimum value, 0.0010 seconds. Press OK and see if this makes any difference to the throttling problem you are having.
The Latitude series has a variety of throttling problems. After you make some adjustments, post a screenshot of the TPL window if you need help.