After Microchip hacked into the Reavers' computer system, Prettyboy, Reese and Skullbuster were sent looking for him and therefore also the Punisher. Microchip took Castle to his cousin, Elliot, who supplied him with a suit of armour that Micro customised and weaponised enough for Punisher to defeat the Reaver gang.
Although that suit was self-destructed for Frank to get the overall upper hand, he defeated the Reavers and would later retrieve another suit to use against murderous junkies taking drugs that gave them superhuman powers. Again, although he succeeded in killing the offending junkies, the suit was disabled due to damage and Frank never used it again.
The Exo-Armour enhances Punisher's human strength to Class 10, it had arm and shoulder mounted cannons and a grapple gun that could allow him to scale buildings in the suit.
The Punisher's Exo-Armour was created by artist Bill Reinhold for then Punisher writer Mike Baron.
Ultimate Universe: on the Earth-1610, the SHIELD black-ops division gave to the Punisher an exo-armor to boost up his human capabilities, giving him strength, speed, and a neural control device to avoid him to disobey the orders. Gently offered by Gregory Stark.