Originally Posted by
Arkat
Correct.
Incorrect.
Universal Spell Power stacks with Potency.
Universal Spell Power stacks with Devotion.
Potency does not, however, stack with Devotion (or any other typical spell powers like Magnetism (Electric), Glaciation (Cold), etc).
Potency is good for casters who do a lot of elemental damage of multiple types because it's easier to fit a Potency item in your gear set than a second, third, or even fourth spell power item.
If you're an Electric Sorc that also does a lot of Cold and Force damage, you'll want a Magentism item to power your Electric spells and a Potency item to help power your other elemental and force spells. Trying to fit a Glaciation (Cold spell power) item AND an Impulse (Force spell power) item can be very difficult.
Things that add Universal Spell Power (feats, enhancements, and filigree for sentient gems are good examples) are great because they stack with the other things that add to spell power whether it's a Devotion item or a Potency item.