The top of the mountain as far as Energy Resistance is concerned, the X-01 Power Armor is definitely in the upper echelon for reasons beyond its level requirements. You need a Fusion Core to power this armor.
Each power armor has a frame and several pieces, they can provide various bonuses like increasing strength, boosting all forms of damage resistance and making you immune to falling damage. Like all other power armors, you'll have to strip off all the actual armor to leave a bare frame before you can get in it.
X-01 Power Armor is a Power Armor in Fallout 76.
