Original gauntlets gave +2 damage and 'ogre strength'
Gauntlets of Ogre Power: These gauntlets give the wearer the ability to strike as an Ogre and generally give his hands and arms the strength of an ogre. They do not necessarily increase hit probability however. (Monsters and Treasure, 1974, TSR, p 38)
Ogre's did more damage in that game than a normal fighting man, doing 1d6+2 (Monsters and Treasure, p. 8) rather than the standard 1d6 damage.
- I have a vague memory of the DM allowing a Fighting Man to use the
Monster Attacking table for a 4 HD monster when he had the
gauntlets on, but that may have been in an AD&D game; we played a mix
of those two editions in college by the time DMG had come out. How DM's ruled on "strike like an ogre" may
have varied by table, but I suspect that the intent was to allow the
wearer to use the Monsters Attacking table where that was in use.
(I'll post an update if I get a good answer at dragonsfoot forums
later).
The strength increase came in AD&D 1e.
In AD&D 1e, the gauntlets began to provide a boost to strength. This was significant - in that edition, increasing one's stats/abilities scores without a magic item or a wish was generally not possible. There were no ability score boosts as one leveled up. (A notable exception being the 1e UA Cavalier who could eventually increase some scores as time and 2d10 rolls added up).
Gauntlets of Ogre Power: A pair of ogre power gauntlets appear the same as typical handwear for armor. The wearer of these gloves, however, is imbued with 18/00 strength in his or her hands, arms, and shoulders. When striking with the hand or with a weapon hurled or held, the gauntlets add +3 to hit probability and +6 to damage inflicted when a hit is made. These gauntlets are particularly desirable when combined with a girdle of giant strength and a hurled weapon. They enlarge or shrink to fit human to halfling-sized hands. (AD&D 1e DMG, p. 145) (Remained the same in AD&D 2e).
When having a Strength of 16 was a big deal (+1 Hit, +1 Damage), getting 18(00) offered +3 Hit +6 damage - a substantial boost to combat power. The ogre itself in 1e got bonuses of that were different from the gloves, however.
If weapon type is used to determine damage/attack, give a standard bonus of +2 hit points to ogres and leaders/chieftains gain an additional +1 / +2 bonus. MM, AD&D 1e, p. 75). {Their base damage was 1d10; in AD&D 2e their damage was 1d10 "by weapon type, +6" per the Monstrous Manual}.
3rd edition changed that to a flat strength bonus of +2
The 3rd edition (WoTC's first edition) added a flat +2 strength bonus.
These gauntlets are made of tough leather with iron studs running
across the back of the hands and fingers. They grant the wearer great
strength, adding a +2 enhancement bonus to his Strength score.
(Gauntlets of Ogre Power - SRD 3.5
D&D 4e: no ability score boost
In 4th edition, there were two variants of the gauntlets - one for 5th/lower level characters and one for 17th/higher level characters (levels in 4th edition went up to 30). At tribality.com, in the article "The Problem of Ogre Power", the author points out that
"Magic Items do not boost ability scores, full stop."
The following was kindly provided by @MirrorImage.
In truth, magic items in 4th editions rarely made dramatic
improvements to a character. Instead, they typically made incremental
or minor improvements. This is in part because obtaining magic items
were in-built assumptions for how characters level up alongside 4th
edition's habit of balance different classes against each other
(sometimes, to a fault).
The 5th level "Gauntlets of Ogre Power" provided two abilities. As a
passive ability, the character "gain[s] a +1 item bonus to Athletics
checks and Strength ability checks (but not Strength attacks)," and as
a once-per-day ability, the character can gain +2 to damage rolls for
the duration of an encounter.
A lightly min-maxed 5th level character (taking character bonuses to
Strength and Athletics when available) could expect to have a Strength
score of up to 21 (+5), a Strength check of +7 (+5 from the score, +2
from "1/2 level"), and an Athletics check of +15 (+7 from Strength
check, +5 for training, +3 from feats), all before applying the
Gauntlets.
D&D 5e: attuned wearer has, literally, Ogre Strength
5th edition literally aligns the gauntlets with the strength of an ogre. From the Monster Stat Block, an ogre has a Strength of 19 (+4 hit, +4 Damage).
STR 19(+4) DEX 8(−1) CON 16(+3) INT 5(−3) WIS 7(−2) CHA 7(−2) (Basic Rules, p. 147)
You could say that the D&D 5e gauntlets have come full circle from the original idea in Monsters and Treasure, in that the item now marries up the in-game strength of an ogre, literally, with the strength that the gauntlets grant to the attuned wearer.
Gauntlets of Ogre Power
Wondrous item, uncommon (requires attunement)
Your Strength score is 19 while you wear these gauntlets. They have no effect on you if your Strength is already 19 or higher.
In the original game, the best strength you could have without magical help was 18 (by rolling for ability scores) or 18(00) (if the Greyhawk rules were used), whereas now ASI's allow a character to increase their strength score to 20 by level 8. This makes the gauntlets very valuable for a lower level character, or for any character that has not maximized their potential strength score for any number of reasons.
How I used them in a D&D 5e one-shot
I made a monk with a strength of 8 (and the athletics skill proficiency)(level 10, 1-shot) and with the two uncommon items allowed took the ogre gaunts and the ring of jumping. I was able to jump great distances and grapple effectively. My unarmed strikes were magical attacks.
I dubbed this concept 'The Boing Boing monk' and had a great time with it. I have since done something similar with a few other monks in one-shots. (In one case using a belt of Frost Giant Strength).
FWIW
Early in D&D, the linkage between the Norse deity Thor's belt and gloves, and the incredible strength needed to wield his hammer Mjolnir, got 'gamified' to require gauntlets of ogre strength and a belt of giant strength to get the most out of the Hammer of Thunderbolts. (Per a comment request from @nick012000)
