The spray on stuff, for the most part, won’t help you. They are designed to work with jackets that are designed to be waterproof. What Scotchguard, Revivex, and the like do is make water bead up on the outside of jackets so the garments continue to breath. Gore-Tex is waterproof, unless the seams are worn or the membrane is torn. But unless they breath (don’t have water completely covering the outside) you get wet from the sweat. So the DWR sprays allow the jacket to continue to breath. On a cotton jacket, water will bead for a bit, then soak in.
The wax from Barbour sounds like your best bet. I’ve seen their jackets and they work well. They don’t breath at all, so you may be just as wet from sweat, however.
Also, if your jacket isn’t designed to be waterproof, all the sprays and waxes may be useless. The way seams, pockets, collars, etc are built may have a lot more impact on the waterproof nature than any coatings you apply after the fact.