The Unnatural Strength value for Brother Elyas, the Dark Angel assault marine, is his standard strength. It does not include the Powerfist's multiplier, so damage with the powerfist does not use the strength value listed on the sheet.
The powerfist has a Strength value of: 4x3=12+2= 14, not the 10 listed on the sheet. Thus, Doing 2d10+14 damage.
I just didn't want people to forget about that. I added a note on the back of the sheet I'm using tomorrow with a 'stat' line for the power fist to make it easier for the player.