Enemies wearing Power Armors in Fallout 4 can be really difficult to defeat now that Bethesda has made the Power Armor really powerful compared to previous games. The Power Armor in Fallout 4 acts as an external suit instead of a piece of clothing like previous games so always wearing one and being ready for Power Armor wearing enemies isn’t always possible especially given how much Fusion Cores they eat up.
So to easily defeat Power Armor wearing enemies you can do two things: Steal their Fusion Core or destroy it.
Stealing is simple, sneak up behind the enemy wearing a Power Armor and you’ll be able to pickpocket their Fusion Core. Doing so will forcefully eject them allowing you to bust lead into them without much protection. For this you’ll need good sneaking stats, relevant perks and some skill. You can also use a Stealth Boy to making sneaking easier.
Destroying the Fusion Core is easier, all you have to do is aim at their Fusion Core using VATS which will one again forcefully eject your enemy from their Power Armor. You can use meds like Jet to increase your chances at hitting the core if you’re further away.
Biggest benefit to stealing is that you’ll keep the Fusion Core while shooting it will destroy it. Not a huge issue if you’re further along in the game.
These forceful ejections will cause the frame to be in the red and if you try to remove any of the components the game will label it as stealing. So if you’re worried if your companions or those nearby will see you steal then what you could do is jump into the Power Armor and remove the components individually in a Power Armor Rack.
So there you go, happy hunting!