What is the name of your state (only U.S. law)? Utah...
Does anyone know if police officers need a separate search warrant to search someones safe during a search warrant? Especially if the safe didn't even belong to the person they had the search warrant for???
That depends on whether or not the original search warrant had language that would have covered an item such as a safe. Clearly, if the warrant was seeking a 45" television set, the safe would be out of bounds. But, if they were seeking drugs or weapons, and the warrant articulated places in the residence - even if closed or locked, then the search would be fine without an additional warrant.
Unless the warrant was
very poorly drafted, it will possess language that would have permitted them to look in the safe.