Earth-123 is the Earth in every Dimension.
Dimension 55[]
In this Dimension, Ben and Gwen both received an Omnitrix and Charmcaster and Nyancy Chan are not a villains.
Dimension 11[]
In Dimension 11, Ben was the only one to receive the Omnitrix but instead of saving people from bad guys, he became a bad guy.
Dimension 24[]
In this Dimension, the Omnitrix was never sent to Earth. Azmuth, the creator decided to keep it for himself and use it for its intended purpose.
Dimension 3[]
In this Dimension, Ben Tennyson accidentally triggered the self destruct mode for the Omnitrix and the whole universe was destroyed because he could not find the creator of the Omnitrix.