The Winchester P95 Plasma Carbine was developed by Winchester as a replacement for the bulky, demanding Plasma Caster. While it ultimately lost out to the RobCo/REPCONN Urban Plasma Rifle, it remained popular with Enclave personnel when they were able to get their hands on one.
After the defeat of the Enclave in the Core Region, the Plasma Carbine was phased out in favor of the Urban Plasma Rifle in large quantities as The Enclave made their way eastward. As such, personnel deployed in the Capital Wasteland never used it as their workhorse rifle.
It had a resurgence of popularity in the 2290's during the Great Patriotic Revolution as a powerful and compact weapon system that performed better than the standard Urban Plasma Rifle in the close confines of Jefferson City, where the Urban Plasma Rifle's bolt was simply too slow to hit moving targets.
It is also used by Enclave troopers patrolling the beaches and exterior of Falls Edge, the Enclave's main and final headquarters.