I don't know how to take a screenshot in Martyr?
Anyway, I found a relic Sniper Rifle with the following enchant:
"The first attack with Surprise bonus deals +292% damage"
However, it deals only 2300 from Suprise state - where it deals 2000 WITHOUT surprise. I tested this on enemies with a large HP pool (7000+) - to make sure they survive the hit.
The 300 extra is probably from the 30% standard surprise attack bonus (should be 600, though - as 30% of 2000 = 600).
So, the 292% definitely doesn't work here - and I guess the normal surprise damage doesn't work either.