Source: Tom Elmhirst: Recording Adele 'Rolling In The Deep'

https://www.soundonsound.com/techniques/tom-elmhirst-recording-adele-rolling-deep

“I recorded all Adele's vocals with my Rode Classic 2, going through my UA 6176 mic pre, and never went back to them. The vocals in the final version are all from the demo. She was really going through something and you can hear it in her voice. I think I also used quite a bit of Logic overdrive on her voice, too, to add harmonics.”