In Fallout 3 the Hellfire power armor can be looted from Enclave Hellfire Troopers in the DLC Broken Steel. In Fallout 4, it's a little easier to obtain from Pyro, a member of the Forged Raider gang.

Fallout 3 introduced training requirements for Power Armor, while Fallout 4 added Fusion Cores as power source. The Fallout show solidifies Power Armor with Fusion Cores as canon, setting the ...