The P94 is a bulky, industrial-grade energy caster powered by microfusion cells. The superheated plasma bolt forms in a special chamber, then sent down a superconducting barrel and stabilized by electromagnetic claws upon exiting it.
In this version, the plasma bolt chamber has been hotwired to accelerate the bolt formation process, resulting in an increase in the rate of fire.
In Fallout 2, the plasma rifle can simply be upgraded by anyone who does so (preferably by Algernon in New Reno). Take note, that the base AP cost was increased from 4 to more standard 5, effectively nerfing it and making the YK42B pulse rifle the most powerful energy rifle, although the Turbo plasma rifle is significantly more accurate (same as a laser rifle).