The advanced power armor Mk II, also called simply Enclave power armor, is a model of power armor used exclusively by the Enclave military forces, developed after the Great War to rival that of the Brotherhood of Steel. It is composed entirely of lightweight composites rather than the usual combination of metal and composite plates. Its design is substantially different from the earlier model using the same designation, but using a different helmet, and lighter materials.
Dialogue of the Brotherhood of Steelscribes suggests that the Enclave's power armor is significantly more advanced than the Brotherhood's, with Brotherhood paladins expressing concern that their standard bullets may not even be able to penetrate it. They also refer to it as "black devil" power armor.
In actual gameplay, Enclave power armor is only slightly better than Brotherhood power armor in terms of damage resistance, though it can take slightly more damage overall before breaking.
Note that its appearance in Fallout 2 is identical to that of the standard advanced power armor. In Fallout 3, the appearance of the armor was mostly changed, but it is still referred to as "advanced power armor Mk II" in dialogue.