Your Strength score is 19 while you wear these gauntlets. They have no effect on you if your Strength is 19 or higher without them.
Notes: Set: Strength Score, Buff, Handwear
It's all ogre now.
If you're a player who has these gauntlets and the DM gives you belt of giant strength DON'T GET RID OF THESE just because the belt gives you more STR. The reason for this is because the DM could be planning to give you the Hammer of Thunderbolts in the future,and that hammer requires you to be attuned to both Gauntlets of Ogre power and belt of giant strength ''any variety''.
It's actually been clarified that you don't have to ATTUNE to the either the belt of giant strength or the gauntlets of ogre power to make use of the Hammer of Thunderbolts. You just have to bear WEARING them. Obviously, just wearing them without attuning to them won't provide you with any of their benefits, and you'd likely want to attune to the belt, as the strength bonus from the Hammer stacks with it. A belt of Fire Giant Strength + the Hammer puts you at 29 strength, and a belt of Cloud Giant Strength + the Hammer maxes you out at 30 strength.