The Power Fist is a very versatile armament. Over the course of various popular sci-fi games, it comes in many different types. Some more deadly than others.
The power fist of this universe is only reserved for the elite of the elite, Adeptus Astartes. It is a very strong weapon and which is probably the reason it doesn't come with many verities or upgrades. The Power Fist increases the users strength many fold and grants the wearer to fight in close combat with a much tougher foe. The weapon itself is a glorified gauntlet that pulsates with power that could destroy the strongest of armors and snap the toughest of bones. Straigestly the Power Fist is used to break up tanks or take down heavy armored infantry in close combat. Like other power weapons in the 40k universe the power fist is installed with a device that causes it to emit a power field around it thus allowing it to disintegrate armour and flesh alike.
In this universe the power fist comes in many different verities and models. One model being the Big Frigger Power Fist, by Beatco (in game war company). Does much as the one in the Warhammer universe but for the standard human and not a super human space marine.