Most of us are using Wi-Fi or 3/4G to get online these days. But there are still many who prefer to connect via an Ethernet connection. Mainly because of a more stable connection + higher transfer rates.
As a Surface RT user it can get a little tricky to use it via an Ethernet connection. Surface RT/Windows RT is very picky on the adapter and is only compatible with the AX88x72A-chipset.
Since Surface Pro is a regular x86-PC you can use any Ethernet-to-USB Adapter. Through Amazon or Ebay you can get them also very cheap.
There might be still some of you, who would like to buy an adapter directly from Microsoft. For those of you there is now the Surface USB to Ethernet Adapter priced at $ 39.99 in the Microsoft Store – currently out of stock.
Source: Surface USB to Ethernet Adapter