Infinite Energy Sources

Mana Breeder Reactor (Slime Tensei) (keeps your magic at max)
Caged Suns (MtG New Phrexia) (Enlessly produces MtG Mana, color depends on color sun purchased)
Chaos Ring (Castlevania Aria of Sorrows) (Keeps supernatural energies at max)
Triforce of Power (Zelda Twilight Princess) (Keeps magic at max)
Origel of Origins (Ar Tonelico) (infinite magic energy generator)
Unlimited Power (Galacta) (Not actually an infinite energy perk. Makes energy costs nothing)
Heart of Green Fire (Shin Godzilla) (ensures you'll always have more of whatever energy you need, so long as your body makes the energy biologically)
Super Chibi (Chibi Robo) (infinite personal electricity. Good for robots, can share with your plug)
Alien Blessing (Chibi Robo) (Same as Super Chibi, but without a plug)
Emerald (Prisma Illya) (Infinite Prana generator. Amount of energy limited by what you can take)
In The End, it's Only Our Strength of Spirit That Allows Us To Go On (Gungrave Overdose, Special Perk) (Lets you keep your energy pools at max. Requires intense desire)
Chaos Emeralds (Various Sonic Jumps. You can get like 36 of them IIRC? Supposedly psychic powered. Limited output of energy)
The One Ring (Exalted Mortal Heroes Gauntlet. Only has 1 mote, but it's still technically infinite. Also you can wear 8 at a time)
Android Race upgrade Perpetual Energy Reactor (Dragonball Z) (Infinite source of KI that rapidly restores your own reserves)

Fairy Heart? (Learnable/Stealable magic in Fairy Tail, can't be bought)
Most of the true magics? (Fate) (IIRC Four of them can be used to just make energy)
Infinite Mana Supply (Fate/ Servant Supplement Skill) (Not sure if it counts. It's a skill F/GO's Prisma Illya has) (works the same as Emerald, as the skill represents Illya having Emerald)