Look here to see what I mean? Should I ask one of these guys to delete their answer (and merge whatever detail is missing into the other answer)? I'm aware of this other question, but it's a little different.
If I am such second answerer myself, even by a split second, then I delete my answer if I recognize it's a duplicate. Hence I do not upvote duplicate answers that are not first. I would not downvote such duplicates though, as one can never be sure what happened in the 5 minute edit grace period.
If the second answerer comments "you just beat me with that" but do not delete their answer, then I tend to comment "there's always the delete link...".
(The timeline of the example you gave shows that the 1st answer did not match the 2nd, until it was edited after the 2nd was posted. In such case, if equal, I'd upvote the 2nd.)
I'd tend to upvote both as long as they are timely close enough to each other: if one answer comes 10 seconds later than the other one, I'd like to show my appreciation to both answerers.
If there are several minutes (hours) between the two answers, I'd downvote the second one since it makes me feel like he (she) just copied the first answer and added a pinch of own content.