Yep, USB 3 adapter. I tested the adapter on my old (beat to hell) laptop running Peppermint, and got the same results that I did in the peppermint live CD. I even plugged it into the USB 2 port on that old laptop and got 150Mb/s average.
I am getting these figures directly from Google's speed test. I am doing local network data transfers (HDD hooked up to the HTPC, Windows drive sharing activated so I can transfer data from the desktop, however that's not an issue as it sits.
Here's the actual adapter:
https://www.amazon.com/dp/B00PC0H9IE/ref=cm_sw_r_other_apa_i_jJx2DbJ9T876D