Hmm, powered armour sounds like a very efficient heat exchange system. Something combining lots and lots of low mass/high bulk armour with superconductors that duct the energy down into subterranian water resevoirs.
Moving out of the game and into the universe, the way I’d deal with a fortress like that is with low mass C-fractional strikes against communicaiton platforms… either that or threaten to commence glassing cities if the planet doesn’t surrender within a given time period. Give them a chance to give up, then chuck rocks directly at population centers daily. Either the populous rises up against the government and surrenders, or they would have been too much of a pain to pacify anyway. Once a continent has been reduced to slag, you can begin landing troops in that blind spot.