Since they are both "suited up aliens", they might be from the same faction? With the glowing eyes, the power suit looks like it could be the terror unit of the spacesuit.
Now we know that space is not simply the vast emptiness between far away, lifeless planets and barely visible stars. It makes one wonder about what may happen to the people who go out there. Accidents occur and astronauts have been witness to strange sights, but can we be sure this is all? Spacefarers are at the boundary between our civilisation and others, and some have been lost. Like we have done before to lifeforms we considered primitive, humans may well have been brought to be shown in faraway capitol worlds. Rumours of odd encounters with beings in spacesuits may now be seen in an entirely different light: as the first step of an infiltration attempt, by a society entirely alien to ours which thought this to be the raiment of our species. What kind of visitor hides in a stolen suit?
Much like the Church Beastmaster in Piratez, the spacesuit could turn into something else on death: whatever you decide is hiding in it. Maybe the suit wearer has glowy red eyes to fit with the power armor? To follow Zane's suggestion: A tortured human, host to an intelligent parasite. And when they realize they did not blend in, they strike, wearing tougher armor of their own design, intent on harvesting new bodies to take over, living or dead: alien can be encountered on research early on, then harvest and terror missions. Spacesuit version has little armor, but good damage modifier/hp since the main human body is not really its own so it doesn't care about damage. Power suit version has more armor, but similar stats otherwise. Maybe it contains enough parasites that, on a melee hit, it infects soldiers/civilians, turning them into the same "zombie" that the suits turns into on death.
It would create a unique gameplay experience, where you have to kill your enemies twice. First destroy the suit (easy for the space suit, hard for the power suit), then the parasite (same unit for both since they are the same "corpse-riders", same too for infected soldiers/civilians). And.. the parasite/abductor/corpse-rider vibe is rather nice and creepy. Add a vulnerability to fire (it is a plant-like parasite, and cooking the corpse is better at killing it than blowing off chunks) to make some unusual weapons shine, probably plasma as well, but not ap/gauss/laser/explosives.
