The Mr. Plankton Universe is the alternate-universe that appears in "The Algae's Always Greener." In this universe, Plankton got the Krabby Patty Secret Formula, and thus, founded the Krusty Krab and Mr. Krabs got the chum formula that was shown in the episode "Friend or Foe."
Difference with Original Universe
In this universe, Plankton is known as Mr. Plankton, and Mr. Krabs is known simply as "Krabs". In this universe, it can be reasonably assume that the events shown in the episode "Friend or Foe" were switched, and Plankton got the Krabby Patty formula, and Mr. Krabs got the chum formula. Another major difference is that Plankton now has a daughter, Pearl.