MTG

Any number of artifact creatures dealing combat damage to a player will generate a total of 2 energy. You're right that the "one or more" text puts a cap on it.

However -- say you have three artifact creatures, and one of them has first strike, but the other two don't. When the first-striker deals combat damage to the opponent, Pia's ability will trigger, and you'll get two energy. Then when the non-first-strikers deal combat damage to the opponent, her ability will trigger again, and you'll get two more energy.

Another way to get more than 2 energy out of her in a turn is to use "additional combat" effects.

Note that you can only get two energy per player, but in multiplayer you could make more by hitting multiple people (EG if you hit Bob with 3 guys and Alice with 1, you'd get 2+2=4 total energy)

If combat damage is dealt at the same time by one or several artifact creatures, then the ability triggers once (you get 2 energy).

If artifact creatures with first/double strike are attacking, you will get a trigger for the first time combat damage is dealt by the first/double strikers, and a second trigger happens for the other artifact creatures and the second times double strikers deal damage (you get a total of 4 energy).

From the Comprehensive Rules:

510.4. If at least one attacking or blocking creature has first strike (see rule 702.7) or double strike (see rule 702.4) as the combat damage step begins, the only creatures that assign combat damage in that step are those with first strike or double strike. After that step, instead of proceeding to the end of combat step, the phase gets a second combat damage step. The only creatures that assign combat damage in that step are the remaining attackers and blockers that had neither first strike nor double strike as the first combat damage step began, as well as the remaining attackers and blockers that currently have double strike. After that step, the phase proceeds to the end of combat step.

Source: https://antifandom.com/mtg/wiki/Combat_damage_step

@UnPassive only if you have double strike. Otherwise the "or more" text limits it no matter the number of creatures hitting