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 contradictionary. This definition prevents logical contradictions.
 * The ability to do anything, this definition leads to logical contradictions.

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

Nigh-Omnipotence
True divine entities of nearly unlimited power that can create conscious beings, new realities or at least warp them to an unlimited extent.
 * 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 kill 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 - Amara is almost omnipotent. Before the creation of the universe, it took God and his four archangels to merely seal her away. Once released she was easily able to overpower and torture Lucifer and caused heavy disturbances in Heaven with little effort. She is said to be able to erase all of existence and recreate the world to her own will. However, she is not able to find God, as he has concealed himself from her, nor was she able to break free from her prison without the Mark of Cain being destroyed.

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 possesion 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.
 * Pagan gods (formerly) At one time, these beings had thousands or more worshipers. This made them among the most powerful beings in the universe, at least in the same league as the archangels.  However when most of their worshipers abandoned them, decreased most of the gods powers to the level of high-level demons and Alpha although some At least just came in the low and medium-level angels level of power.

Extremely powerful
Entities of immense power, that can apparently warp reality or destroy and create things to a limited extent.
 * 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.
 * Metatron (temporarily) - Empowered by The Word of God, his angelic powers were greatly enhanced and common angelic weaknesses like angel blades or holy fire proved to be ineffective against him, but he was still very far from nigh-omnipotence.