Sorry for more questions on this card, but we’ve been trying for the various Ruins of Atlantis story challenges 
(We got Secrets of the Past just now).
I assume that when Atlantean Font of Power flips cards like Lightning Reflexes, Fleet of Foot, Impromptu Invention, by following the instructions on the card, you are allowed to play additional cards (from your hand) out of turn?
Similarly, I assume that when it flips cards like Flame Spike, Unload, and Smite the Transgressor, by following the instructions on the card, you are allowed to use powers out of turn? (Flame Spike and Smite the Transgressor each granting 1 power total, since 0 normal + 1 additional = 1).
We were able to get the story challenge without playing it as above (to be safe), but we wanted to know if it could have been easier (Expatriette flipped Unload).
I’ve always played that you could play other cards and use powers out of turn.
The simple answer is that the card is simply played, following the exact wording of the card. If the card says you can/must play a card, you can/must play a card. If it says you can/must use a power, you can/must use a power. Issues that may come up is when the card says you can play an additional card this turn or you can use an additional power this turn, given that it is currently the end of the environment turn. There is currently no Play or Power phases, adding an additional play or power may have no affect. Or it could be ruled that the additional play/power is used immediately. Or it could be ruled that the effect does not occur until that player’s turn. (My guess is that it has no effect, at least that’s how I’d play it if one of Tachyon’s ongoing cards plays stating she can play an additional card this turn.)
Actually, you shouldn’t have to worry too much about most of the Ongoing/Equipment cards. Upgrade Mode, Assault Mode, HUG Goggles, Pushing the Limits, and Legacy Ring all say that you may play an additional X during your X phase. So I assume those have no effect, since it isn’t currently your X phase. You just got to play them early for next turn. Oddly, only Utility Belt says “You may play 1 additional power each turn.”, but I’m sure that’s just an unintentional inconsistency. All of the One-shots say “this turn”, which is why I assumed it worked the way I stated (allowing you to play out of turn).
But yes, what you said is the crux of the fuzziness. Does “you may play an additional card this turn” work on a turn in which you could not originally play a card? Again, my guess is 0 + 1 additional = 1, but I could be wrong.
(We got Secrets of the Past just now).