-수 / -수다 is a polite sentence ending from outside standard Seoul speech — old-fashioned Seoul in 할 말 있수 'I have something to say', Jeju in 왔수다. Half the lines collected here are simply the title of the drama 폭삭 속았수다, and two more are joke respellings of -습니다 (보겠숨돠, 괜찮숨니다). That shows the ending exists, but it is not enough to pin down when a speaker would actually choose it.
Register: regional or old-fashioned
The examples below did not fully pin this one down — read them before relying on the entry above.