From my experimentation - it seems to be random with nearly everything [rewards, chests, non quest specific items, etc]. You can literally save/restore to try and hit the jackpot [ie: jewelry with just the right stats you need for your character].
I think loot that isn't specific for a quest is randomised. I remember loading after death and reopening an urn, discovered i got a different prize than the last time.
Let us swim in this sea of fire, and hope that the demons of doubt do not drown us.
