elemental amp/boost + Accessories/equipments

[Reeeeeeeee]

do they stack ?

[Shinigami Miroku]

Boost + Amp stacks
Boost + Boost does not stack
Amp + Amp does not stack

[Arifufu]

yes, i can confirm:
Kagutsuchi Vow (50% fire damage) + Fire Amp (50% fire damage) = 100% fire damage boost, if u doubt u can use Oven Vow instead that increase 40% fire damage so 90% fire boost instead.
however in P5R (element) Amp + (element) Amp won't stack, but in P4G u can take my word they do stack, in P5R there's no element damage range from 10% - 50%, only choice between 25% and 50% for P5R, so don't get mix up.

Frost Shot (Naoto weapon, 25% ice damage) + Kuraokami Vow (50% ice damage) = 75% ice damage boost

Perun Plate (Kanji weapon, 25% elec damage) + Elec Amp (50% elec damage) or Takefutsu Vow (50% elec damage) = 75% elec damage boost (i prefer elec amp because Kanji can learn it and i put God's Love on Kanji)

(element) Amp + (element) Boost = 75% (element) damage boost