Omnipotence

There are different definitions for Omnipotence: The problems occur by asking questions like "Could God make a stone so heavy he can no longer lift it?" If he can't do it, then he is not omnipotent because he should be able to create such a heavy stone, if he can do it, then he is not omnipotent, because he can't lift the stone. There are many variations of the problem, for example: Could God create something stronger than himself ? As no character in the Supernatural Universe is omnipotent by either of these two definitions, no such problem has arisen on Supernatural.
 * The ability to do anything non-contradictory. This definition prevents logical contradictions.
 * The ability to do anything, this definition leads to logical contradictions.

Omnipotence
No entity in the Supernatural universe is truly omnipotent in the sense of the common definition of the word.

Nigh-Omnipotence
Primordial entities of nearly unlimited power that can create conscious beings, new realities, or at least warp them to an unlimited extent.
 * Cosmic Entity - Cosmic Entity is the oldest being in the existence. It rules the Empty, a place of nothingness inhabited by every deceased angels and demons where they slumber for all eternity. The Entity has unrivaled control over it, even Heaven, Hell and God does not have authority on the Empty. Like the inhabitants of the Empty, the Entity itself sleeps eternally and unlike them, it needs to sleep. If any being is awakened in the Empty, it affects the Entity and awakens it from the eternal sleep which causes it pain. Despite his complete authority over the Empty, the Entity cannot force a being to sleep.
 * Death - Death holds immense power which is far greater than Archangels. According to himself, he would reap God at the end of time. However, there are many things he can't do.
 * God - God possesses near-infinite power, being able to do almost anything that he desires. It is shown that he isn't fully omnipotent, as he can't instantly kill his older sister, the Darkness. However, through his own power, he was able to create beings who helped him defeat her, although barely. Being almost omnipotent, he also has the ability to give himself more abilities, among those were the ability to speak French and play guitar.
 * The Darkness - The Darkness is the most powerful entity in existence, more powerful than God himself. The latter, her younger brother, stated that even with all four archangels fighting against her the first time, along with himself, victory was barely achieved. Even after withstanding a combined but sequential attack by powerful supernatural beings during a second confrontation, she still proved to be stronger than God when she stopped him from trapping her again, overpowered Lucifer at the same time, and fatally wounded her brother, all before regenerating fully and walking away. Not long after, upon reconciling with God, Amara was able to heal the fatal damage her nigh-omnipotent powers did to him, without any difficulty.

Lower Tier Nigh-Omnipotence
Entities of nearly unlimited power that are weaker than the top tier.
 * Archangels - Archangels have a tremendously vast supply of power, they can accomplish incredible feats of power such as obliterating and banishing common Angels with gestures, finger snaps, winks or even simple thoughts. However, there is still much that they can't do: find humans who are protected by enochian sigils, forced possession of a vessel, or breaking out of Lucifer's cage.
 * Castiel (temporarily) - Castiel's powers were exponentially magnified as a result of having absorbed all the souls from Purgatory. At this level of power, Castiel could annihilate lower Archangels with a snap of his fingers and (supposedly) erase Hell from existence. However, he was still keen on keeping Michael and Lucifer locked in the Cage.
 * Metatron (temporarily) - Empowered by The Word of God, his angelic powers were greatly enhanced and common angelic weaknesses such as holy fire proved to be ineffective against him.

Extremely powerful
Entities of immense power, that can apparently warp reality or destroy and create things to a limited extent.
 * Jack - Jack is the son of Lucifer, a Nephilim possessing unimaginable power. According to Sam Winchester, his powers will surprass Lucifer's. Currently Jack is a newborn Nephilim therefore does not have control over his powers. He was able to awaken an angel sleeping in the Empty unintentionally, which was impossible according to Entity controlling the Empty and was surprised to see an awaken being.
 * Jesse Turner - Fueled by Lucifer's presence on Earth, Jesse has accomplished incredible feats of power such as exorcising a demon by verbally telling them to leave their host, turning an Angel into a figurine, conjure beings into existence simply by believing in them, etc. According to Castiel, at the peak of his power, Jesse would have been able to destroy the entire host of Heaven with a single word.