Power Fist: The cestus, yes; the spiked gauntlet, yes; the electro-zappy-glove, yes. The true power fist, however, as seen in Fallout, et. al., generally comes attached to a set of Powered Armor, or at least a power torso – in the interest of not ripping your arm off when you try to be Ms. Punchy – sorry, Veronica – or at least straining something quite badly.

(This rule is, of course, void for appropriately built cybershells.)