Chaos energy

The unpredictable and unlimitless power from the seven Chaos Emeralds. However it can be controlled by the Master Emerald if requested or commanded by it's Guardian.

The Chaos Emeralds, especially the Master Emerald have been used before to charge Sonic or Eggmans weapons of destruction many times. (E.G Sonic the Hedgehog 2 where Eggman steals the Master emerald to charge the Death Egg.) But the chaos energy comming from the Master emerald is mostly used to prevent Angel Island from falling into the ocean and to keep it floating.

Sonic Adventure
In Sonic Adventure the original guardian of the Master Emerald is Chaos who also guarded the Chao that lived in peace at the alter that shrines the emeralds. (Origins of Chaos explained on his article.)

Tikal also remembers a prayer her grandmother used to say:

'''The servers are the seven Chaos Chaos is power, power enriched by the heart. The controller serves to unify the chaos.'''

By Controller it could either mean the Master emerald or the Guardian that controls the emeralds through the Master Emerald.

When ? is unlocked, it will show that Chaos will absorb the negative energy of the Chaos Emerald leaving only the possitive energy. Sonic uses the remaining possitive power of the Chaos Emeralds to become Super Sonic. This shows that they have an Electromotive force but can still be of use if the possitive or negative energy is absent, such as Super Sonic needing only the Possitive energy or Perfect Chaos relying on negative energy.

Sonic Adventure 2 and Shadow
Shadow was awaken by the power of a Chaos Emerald and demonstrates harnessing the power of Chaos emeralds for such powers lie Chaos Control, and later stocking the Eclipse Cannon with the emeralds for another doomsday plot.

Shadow shows that chaos energy can be harnessed for other means other than Super Transformation such as Chaos Sphere and Chaos Blast and also to unlock memories.