How does multiplying damage work in Skyrim?

While wielding a daedric dagger, having 100 one handed(all perks) and 100 sneak(all perks), the daedric dagger's base damage showed as 33. From the dagger's sneak attack(only 15x damage) it caused around 500 damage. Then I applied a power attack and it caused 1,000 damage. Then my orc used berzerk and a single strike caused 2,000 damage.

I could do some more testing (like getting shroud gloves, dual wielding with a power attack doesnt do a single hit unfortunately), and having bonus one handed damage enchants(it modifies the displayed base damage btw), but I think this is enough to show that multipliers stack (15x + 2x = 30x + 2x = 60x) instead of combine(15x + 2x = 16x + 2x = 17x).