Slow internet speed with an ethernet adapter on my Mac

You can’t evaluate adapter performance by measuring Internet latency and throughput because those things change - like the Network congestion and load of your service provider at that tine. You need to do this internally where you control the variables.

Your question is very similar to this one: What dowload speeds is the Apple USB Ethernet Adapter capable of?

You need to use the iPerf3 utility to measure the performance internally. It’s free snd simple to use.

As for differences in performance, it comes down to the quality of the USB bridge in the adapter and the quality of the Ethernet chip itself; they’re not all created equal. High quality USB to Ethernet adapters will have low latency (ping results) and higher throughput (iPerf3 results).

In your example, the variance in your ping results - 12ms vs 24ms could be due to the quality of your adapter and/or inherent latency of your internet connection. USB speeds and feeds have nothing to do with this. Same for your transfer speeds - what you’re seeing is well below USB 2 throughput. However, it can be affected by the quality of the adapter and/or the inherent throughput inconsistencies of the Internet.

I actually address the “quality” issue in this post: AX88179 ethernet adapter keeps dropping connection. As far as the comment re: Apple branded Ethernet adapters, the answer is any quality adapter with a compatible chipset will work and perform just fine. Avoid the inexpensive off brand adapters and stick to brands like Belkin, Anker, Netgear, etc.

Setup a small test environment as described in the linked answer so you can eliminate the unreliability of the Internet connection and limit your test to variables you can control.

In my experience it is not so that only the Apple made Ethernet adapter works with Macs. I have used various 3rd party Ethernet to USB-C adapters and even Ethernet to Thunderbolt adapters (both in docks and in dongles) - and haven't had speed issues with them.

In general a USB 2.0 adapter is not going to allow you to transfer data at ful gigabit speeds. However achieving 150 Mbps should not be a problem. USB 2.0 has a theoretical maximum transfer rate of 480 Mbps, but in practice I would expect a USB 2.0 Ethernet adapter to max out at about 300 Mbps.

You can unlock the full potential of gigabit ethernet by using a USB 3.0 or Thunderbolt 2 Ethernet adapter instead.

I would start by checking the actual configured speed on the adapter. In the Network Settings (your screen shot) - choose the USB Ethernet adapter and click Advanced.... In the window that comes up, choose the Hardware tab and check that the Speed setting is set to the maximum possible. Usually setting it to configure automatically should do the trick.

Another thing is to try different cables, switch ports, etc. - however as you say that you're using the exact same cable with another computer that achieves better speeds then it is probably not going to help.