I’m reasonably sure this question has been answered already, but I can’t find the relevant thread at the moment, so sorry for asking again.
Do procs of the same item stack, as in, do I get twice as many procs (when using two Empowered Starfire Rings for example), do both procs share the same cooldown or do I get nothing at all from the second item? Also, does this mechanic differentiate between weapon procs (e. g. Chain Lightning procs from various weapons) and equipment procs since weapon procs are generally only triggered by attacks of that very weapon?
What happens when I use two different items with the same proc (e. g. Stormheart and Crystallum)?
They stack. You get 2x as many procs. If they have CD, then proc from each item uses his own, independant, CD. Procs from weapons are no different from procs on any other gear piece.
There is a category of procs, named Weapon Pool Skills (WPS).
WPS can be triggered ONLY with default attack, or skill tagged as “default attack skill” (Savagery, Fire Strike, etc). WPS “augment” your “default attack” (unlike normal procs, that work independantly).