USB-C 2.5G ethernet LAN adapter limited to 1000BaseT but only when power adapter is connected

I have a strange issue when trying to use USB-C 2.5G ethernet LAN adapters with my 2019 Macbook Pro 16-inch running Ventura 13.6.1. I first tried a cheaper Acogedor adapter and thought it was maybe faulty because it wouldn't do 2.5 Gbps. I returned it to Amazon and ordered an Anker A8316 Power Expand USB-C to 2.5 Gbps ethernet adapter only to find the same issue. I then tried a process of elimination. Was it my newly installed wall jacks or the cat6 cable run from the basement?

I took my Macbook to the basement and directly connected with cat6 cable to the 10G port on the modem. Ah, hitting 2.5 Gbps here! Went back upstairs and tried one more time from the wall jack. Oh, that's peculiar - I now have 2.5 Gbps here as well. After some time, the problem happened again...limited to 1 Gbps. What is going on? I even went so far as to re-terminate my wall jack upstairs. No luck.

Suddenly I realized... This is only happening when the AC power adapter is connected to the Macbook. (That's why it worked when I temporarily took the Macbook to the modem in the basment...on battery power). I would see this while running on battery:

Then upon connecting the power adapter (the original one that came with the Macbook, no third party), the LAN connection would drop out momentarily, then reconnect and I see this:

If I try to manually configure, it defaults back to autoselect speed as soon as I click OK.

If I unplug the AC power, it remains limited to 1000baseT until I disconnect then reconnect the adapter, then it's back to 2500baseT.

I've tried using different combinations of ports, or going through USB hubs. I even have a Boot camp installation of Windows 11 and the same problem occurs there as well. So I guess this can maybe be narrowed down to either the two USB-C ethernet adapters being made with the same components and they don't play nice with the Macbook (I've got a third one from Plugable on the way to try that out, will report back here), or, perhaps this is something to do with the Macbook USB ports themselves or an issue with my AC power adapter? I don't know if I'm ready to buy a whole new power adapter just yet for a try and see...unless someone here knows for sure that would definitely be the culprit?

I'm guessing I can rule out that it's something with the OS if this happens on both Ventura as well as the Windows 11 side? Unless both OS's have the same driver issue or something?

Looking forward to any ideas for solutions and discussion here, as I am genuinely stumped!

Cheers