Electro attack

The Electro attack was a built-in Cyberman weapon, demonstrated by both types, as well as the Cyberslaves on different occasions.

Cybermen of Mondas
It was first used by the Cybermen of Mondas, in their attempts to take the Moonbase, and was later used again by the same sort of Cybermen after being awakened from their Tombs. The attack involved firing a discharge of electricity that almost instantly knocked any human out cold. (TV: The Moonbase) Although stronger, humans sometimes took more than one blast. (TV: Tomb of the Cybermen)

The Cybermen encountered by the Twelfth Doctor on a colony ship on Floor 1056 possessed this form of attack, able to electrocute him to near death when one grappled him, almost forcing a regeneration. It left him unconsciousness and unable to walk properly despite trying to recover for several weeks, less during the actual skirmish on floor 0507 though. (TV: The Doctor Falls)

Cybermen of Pete's World
A different version of the Electro attack was the first weapon exhibited by the Cybermen of a parallel universe. It involved an electrical discharge delivered to the victim through the Cyberman's gauntlet. The shock was enough to kill a human instantly. This weapon was usually used (on humans) in the neck or shoulder region to ensure death was instant. The electrical discharge was blue in colour. They could apparently choose whether or not to employ it, as several Cybermen were able to grab individuals without giving them a lethal electric shock. (TV: Rise of the Cybermen/The Age of Steel, The Next Doctor)

The Eleventh Doctor could survive it, knocking him out for only a few minutes. The arm that harmed him was severed from its body and heavily damaged though. (TV: The Pandorica Opens)

Danny Pink, while as a Cyberman, used the electromagnetic pulse in his hand to knock Clara Oswald unconscious. (TV: Death in Heaven)

Cybermen in GSO and Cyberslaves
The Cyberslaves at the GSO geological survey, once fully converted, were able to shoot electricity out of their hands and able to kill by touch. The Cybermen, once reactivated, were able to kill by shooting from a permanently mounted gun on their right arms, resembling the Mondasian version. (GAME: Blood of the Cybermen)

Behind the scenes
Non-narrative information in Doctor Who: Battles in Time magazine gave more information about the electro attack.

According to DWBIT 17, although their wrist blasters had no effect on the Daleks, the Cybermen were able to use their electric attack to destroy the Daleks by ripping their Dalekanium domes off.