The ability to have an unlimited amount of energy. Variation of Infinite Supply.
The user possesses an unlimited energy source that will never run out, allowing them to use attacks and accomplish other feats that require energy indefinitely. The source can supply any form of energy, such as electrical, kinetic energy, etc, which can provide power to a physical body, technology, etc. Different types of energy has different affects the users, for example life energy, which effectively grants the user unlimited regenerative power and eternal youth.
After being implanted with the Mantra Reactor, Asura (Asura's Wrath) was able to channel an infinite amount of Mantra without fear of it backfiring and destroying his body.
Due to the Uranium-235 core that animates and powers his body, Adam (Buffy the Vampire Slayer) has a supply of energy that lasts "essentially forever", allowing him to go indefinitely without food, water, or sleep and heal from any wound, even beheading.
Priscilla (Claymore) possesses an infinite amount of demonic life energy, which grants her transfinite stamina and the ability to regenerate from all wounds instantly, which combined to her lack of weak points makes her nigh-indestructible.
Captain Atom's (DC Comics) connection to the quantum field enables him to draw upon infinite amounts of energy, allowing him to use it for purposes which are solely limited by his willpower and imagination
Android #18 (Dragon Ball) possesses an infinite energy supply, allowing her to fight indefinitely without ever tiring.
Prelati's Spellbook (Fate/Zero) is both a spell-book and a perpetual prana generator, constantly producing an everlasting supply of magical energy unless destroyed.
The Triforce parts (The Legend of Zelda) grants its chosen bearers tremendous power, especially the Power that granted Ganondorf infinite energy.
Tohru (Miss Kobayashi's Dragon Maid) generates her own mana...
...while other dragons need to convert it from other sources.
Jūgo's (Naruto) body constantly absorbs natural energy, granting him an infinitely growing supply of life energy to use as he pleases, though it also corrupts his sanity from time to time.
Mukade (Naruto) drawing from the infinite Ryūmyaku chakra to regenerate at an immortal rate, so long as the source remains open for him.
Victini (Pokémon) can produce an infinite amount of energy that it can share with others, ensuring absolute victory.
Haja (Rave Master) possesses the Type-61 Dark Bring that gives him infinite magical power.
Hexadecimal (ReBoot) possesses transfinite power reserves, which, though not absolutely infinite, is larger than all finite numbers, allowing her tremendous feats and destructions.
The Chaos Emeralds (Sonic the Hedgehog) are objects of great and mysterious power: just one of them is powerful enough to power a machine at infinite scales (if not overload some) and all seven could destroy the Earth.