Slow internet speed with an ethernet adapter on my Mac With the internet connecting to my windows laptop, the ping/download/upload speed is 16ms/157.15Mps/10.21Mps. However, when I connect the same internet cable to a USB 2.0 ethernet adaptor and then to my MacBook Air (2017 model), the ping/download/upload speed is just 24ms/30.07Mps/10.00Mps. This speed is even slower than the internet speed when I connect to wifi.
In this post, I see some comments suggesting that only Apple's brand of ethernet adapter works for MacBooks. Can anyone give me advice if that comment is right or any other possible solution to fix the slow internet speed when using an ethernet adapter? Appreciate!
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.