Hello,
Could you clarify how will you be connecting the USB-Ethernet adapter? If you're going to connect it by plugging in the USB part into the PC or any end-device and the Ethernet (RJ45) part will be plugged in to the RUTX11 then it should function by default - the most important thing in this case would be the end-device ability to load/install the driver for any specific adapter.
If you'd like to connect USB part to the RUTX11 and the Ethernet part to any end-device, I'm afraid it won't work. It may be possible to make it work with specific adapter which has OpenWRT-based drivers (and potentially some extra tinkering with the RUTX11 itself would be necessary) but our devices do not support such functionality by default.
Best regards,
Tomas.