My take is that Stark had to crudely discharge the excess energy before his suit overloaded. JARVIS could have said similar with another line after stating that power levels were at 400%, but we got what we got. I’m sure that the energy discharge was more powerful than Stark’s normal top end, but not, say, 4 times as powerful. Maybe 150%, which is still quite a whallop - sort of a controlled dump of energy without having this discharge itself destroy any part of his armor. Stark may have designed his repulsors to surge into overdrive in emergency situations, but that’d put a strain on the components (which he was likely repairing late, on the helicarrier, before he got a newer suit in front of Loki’s back).
Of course, all of this speculation is null and void, given the physics of a comic book universe.
Actually, perhaps he should have remembered the two experiences of Thor’s lightning charging up Tony’s suit in A1 and (super) charging the Cradle to finish the creation of Vision in A2, and considered it counterproductive for him to add lightning to Vision & Iron Man’s beams when they were finally weakening Ultron (enough for Hulk to knock him a couple miles away).
Oh, but maybe he did remember – and reversed the polarity on Mjolnir’s electrical charge. He just had to flip one of those switches on the handle, right?
