My answers on SuperUser get different points from upvoteds.
One get 5 points and other one get 2 points. (no downvotes)
Why is this happening?
Chances are these were due to the rep limit.
If you were at 195 (e.g. 18 upvotes + 1 accepted answer) the next upvote would be worth 5.
If you were then downvoted (putting you at 198) the next upvote would be worth 2.
EDIT: I hadn't spotted the 'no downvotes' bit before. Are you sure? What do my reputation tracker show? (On phone, so can't do links easily, but http://csharpindepth.com/StackOverflow/ReputationTracker.aspx should get you there.)