The Powerpuff Girl's and Samurai Jack take place in the same universe.

This make's sense, since Professor Utonium, and Jack look almost exactly the same.

There is also an episode that show's what look's like a destroyed city that resemble's the city of Townsville in The Powerpuff Girl's. There is also a billboard advertising dog food on both show's.

One of the Powerpuff Girl's villain's was probably going to commit a serious and big crime. And the Powerpuff Girl's got into a fight that almost destroyed the world. Witch lead's us to Samurai Jack.