Two-part epoxy primers should not be used over one-part topside paints, or over paints that are unknown. The solvents used in two-part primers (or even paints) may soften or destroy the underlying paint if it's a one-part paint. Only apply a two-part primer if the existing paint on the substrate is a two-part paint.
If the paint type is unknown, it's not recommended that you gamble and end up with a big mess and a lot of money wasted.