What are the rules for combining elemental damages from different sources?

[Timothy McNeil]

I apologize if the answer to this is effectively right in front of my eyes and I cannot see it while perusing the rules.

My question is can the elemental damage from an Eidolon's Energy Attacks evolution be combined with something like an Amulet of Mighty Fists (insert energy type here) to deal 2d6 points of selected energy damage or would such a pairing still only result in 1d6 points of selected energy damage if the same type is selected?

Thanks.

[Shifty]

I haven't seen a rule that says they don't stack.

[Michael Foster 989]

they are different sources (item and feat) so they would stack as they are both untyped bonuses to damage