Keystone of Bezel (Ben 10) increases all of the natural powers, abilities, and skills of the possessor, and increases the power of the charms tenfold.
The Ecto-Skeleton (Danny Phantom) amplifies Danny's ghost powers by 100x.
Elize Lutus (Tales of Xillia) is able to access high-level spirit artes and magic using her booster, Teepo.
Even a single shard of the Shikon Jewel (InuYasha) can greatly enhance the user's powers.
The Double Gear System, (Mega Man 11) is device developed by Dr. Wily. The Power Gear and Speed Gear of the device were able to give the robots who use them "unstoppable power and insurmountable speed".
The Chaos Emeralds (Sonic the Hedgehog) are able to empower beings when all of them are collected.
Master Emerald (Sonic the Hedgehog)
Turles (Dragon Ball Z) holding a fruit of the Tree of Might.
The Dragon Medallion (Mortal Kombat) enhances the owner's powers to omnipotent levels.
Demon's Blood Talismans (Slayers)
The Death Totem (Arrowverse/DC Comics) can act as a power booster for dark magic.