G6 ZBOOK will not charge when mains lead is connected

[MNMO]

My G6 ZBOOK is no longer running on mains ac power. I noticed this morning (29-3-24) that the mains adapter lead, although connected and powered up,  is not charging the laptop. This was working fine previously. So I checked the mains power adapter outlet plug (that fits into the power connector on the laptop) using a simple digital multi-meter, and it shows 19.89 Volts DC. However, when plugged into the laptop mains adapter socket it isn't charging and the laptop is therefore only able to run on battery power which is currently 63%. The mains power socket on the side of the laptop appears to be OK visually. When I connect the powered up mains adapter lead, the indicator light (Battery light) flashes white 8 times then goes out. However, when followed by switching the laptop on - it still only runs on battery and does not indicate that mains power is connected.

Next thing I did was to download and run the official HP DIAGNOSTICS TEST to test the battery and mains adapter.

Test 1. The Batter test passed OK. Power not at 54%.

Test 2. The mains adapter, although connected and powered, was not recognized. (message given was 'please connect a mains adapter (as best I can recall) Does that indicate a faulty mains adapter?

SO,  I am wondering

1. is 19.89 volts too high and above the acceptable limit for this laptop such that the laptop will not allow mains power through? in other words, do I have a faulty mains adapter?

2. Is the mains adapter socket itself, the component (whatever that consists of) inside the laptop faulty and in need of replacement?

The only thing I have recently done with this laptop is to install Windows 11 at the weekend (i.e. a few days ago) and I have to admit that I paid no attention to the mains power adapter or power indicator in the status bar so it's possible (???) that its something to do with that OS upgrade??

Any helpful comments by a suitably competent person) would be most gratefully appreciated. Thanks in anticipation.

[I am in the UK and it's 10:29 am]