Power armor is an advanced armor that can effectively block gunshots, cuts, blunt trauma, or burns.
It provides better protection, especially against blunt, and can block heat damage. It also covers the limbs in addition to the torso.
However, it is much more expensive, needs a long time to make and also needs the Powered Armor research before being available. It also provides a movement speed debuff and a work speed penalty of 10%.
It forms a full set of armor along with the Power armor helmet.
Power armor is a huge step up from the armor vest. It provides much better protection than the vest, and covers more of the body. However, it is much more expensive to make or buy.
It occupies both the overgarments, middle, and shell layers, while armor vests only occupy the middle layer - meaning it can't be worn with tribalwear.
Due to the great cost and the penalties, it is only recommended on your most dedicated fighters.