Surface Ethernet Adapter allows you to connect your Surface to a wired network using the Ethernet Adapter. Plug the Ethernet Adapter into your USB port to get online, share files, and print. This adapter was previously not working with Surface RT device, now according to Microsoft Support page, Ethernet Adapter will work with your Surface RT with Windows 8.1 update.
To use the Surface Ethernet Adapter with Surface RT you’ll need to update to Windows RT 8.1 and check Windows Update.
Ethernet Adapter Compatibility:
Surface RT and Surface 2 are compatible with devices that are certified for Windows RT 8.1. Surface Pro and Surface Pro 2 are compatible with devices that are certified for Windows 8.1.