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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

MacBook Pro (2017 – 2020)

Posted on Nov 18, 2023 4:05 PM

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Posted on Nov 21, 2023 7:15 AM

UPDATE: I tried a third adapter, the Plugable USBC-E2500, and so far it works as expected with full 2.5 Gbps speed, on both battery power and AC power! So the problem I was having seems to be a compatibility issue with the Anker and Acogedor adapters which must be based on the same components. They advertise that their adapters work for 2019 Macbooks but apparently that doesn't mean full functionality when your Macbook is plugged into a power outlet.


Long story short - save yourself a headache and go for the Plugable 2.5G ethernet LAN adapter.

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Question marked as Top-ranking reply

Nov 21, 2023 7:15 AM in response to jt0285

UPDATE: I tried a third adapter, the Plugable USBC-E2500, and so far it works as expected with full 2.5 Gbps speed, on both battery power and AC power! So the problem I was having seems to be a compatibility issue with the Anker and Acogedor adapters which must be based on the same components. They advertise that their adapters work for 2019 Macbooks but apparently that doesn't mean full functionality when your Macbook is plugged into a power outlet.


Long story short - save yourself a headache and go for the Plugable 2.5G ethernet LAN adapter.

Jan 8, 2024 7:11 AM in response to JoshHibschman

Sorry, I’m not sure I understand your question. I didn’t expect anything to have to be powered over the Ethernet connection, so I’m guessing your use case may be different than mine? I was using two separate adapters; the original AC power adapter to charge the MacBook, and then the USB-C Ethernet adapter on a completely separate port for wired internet connection only.

Jan 8, 2024 7:52 AM in response to JoshHibschman

Ah I see. That is beyond my knowledge. All I knew was I had to have it connected to my Bell Giga hub on the 10G port. I did not expect that it would also be charging my MacBook and I also did not see that that was the case, otherwise would it not show on the battery indicator that the battery was being charged while connected to the Ethernet only? Doesn’t seem to charge it that way.

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

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