No, not all Enclave soldiers use power armor. Even going back to Fallout 2 which introduced them, a good portion of the personnel at the base Navarro wote combat armor.

advanced power armor Mk II
The advanced power armor Mk II, often simply called Enclave power armor and nicknamed Black Devil armor by Brotherhood paladins is a high-end model of power armor used exclusively by the Enclave Department of the Army and developed after the Great War and the destruction of the Enclave Oil Rig in 2241.

A heavily modified suit of standard Mark II armor used a long time ago by the Enclave, the most noticeable difference is the Tesla device rigged to the suit, with five attraction coils mounted on rounded shoulders.

There isn’t much to say about the Remnants power armor. Its the best power armor in the entire game, granting 36 total damage threshold when equipped. This armor also provides +1 Strength, +20 Radiation resistance, and -1 Charisma.

After the Great War, the T-51 was utilized by various wasteland factions including the Brotherhood of Steel, mercenaries, and the Enclave.

X-01 power armor is a prototype model of power armor developed by the United States shortly before the Great War. It was the last and most advanced model of power armor developed before Great War, and serves as the predecessor to all post-War models of advanced power armor used by the Enclave.

Quests. Arrival at Zion: The player character must speak with Graham to complete the quest. Flight from Zion, Crush the White Legs: During the final quests in Honest Hearts, Graham will become a temporary companion to the Courier.

Damage Threshold
J.E. Sawyer. Fallout: New Vegas mostly moves away from the exclusive use of Damage Resistance (DR) in Fallout 3, towards Damage Threshold (DT). Like in previous games, DT can function as an outright subtraction: if a shot is fired with a damage value of 40 against a DT of 10, then 10 damage will be ignored.

Oakshield. Jun 17, 2020 @ 10:52am. I’m quite certain that for certain power armour types the “T” stands for “Trash”

Yes, T-60 is canon and better than T-51.

Hellfire armor
Hellfire armor The most advanced power armor variant in the wasteland is the Hellfire powered combat infantry armor, developed based on regular power armor designs. A prototype version was developed shortly after the Great War by the Enclave stationed at The Whitespring Bunker.

They are identical in appearance to Enclave power armor and helmet. In comparison with those, their stats are nearly identical except for increased item hit points and values as well as a decreased Damage Resistance on behalf of the Shocktrooper helmet.

With the ability to install not just your preferred Power Armor modifications, but an entirely new modification, Storm Servos, a mechanic to allow Enclave soldiers to move quickly in battle, and allow intense bursts of speed – yet at the expense of it’s wearer’s health.

Also, while the Atom Cats would love to get their hands on a rare model from the second Enclave – the only extra coat, currently, for the X-02, is the Squad Sigma coat. The colors of the most elite, yet the most ruthless squad of the Enclave – who have now, thankfully, been consigned to history.

Now it’s armor finally returns in Fallout 4 as a medium-level Power Armor. In a Red Rocket Station in the middle of the Glowing Sea you can now find this armor.