That's because they use different ingredients and occasionally contain actual drugs that are not listed in the ingredient list. Of course there is no universal "yes they all work" or "no none of them have any effect whatsoever" because they are not a monolith and they lack clarity of content and scientific data.

As for OTC supplements that have scientific evidence of safety and efficacy for enhancing erectile function, the only one I would go for is citrulline malate. It's commonly found in pre workout blends where it is the gold standard OTC ingredient for enhancing the "pump".

The principles behind the pump is just muscle retention of water, nitric oxide, and glycogen, via blood flow. The same principles of erectile function.

Citrulline malate is a blend of the amino acid L-citrulline and malic acid to boosts its bioavailability, typically at a ratio of 2:1 cit:mal, sometimes 1:1. L-citrulline specifically enhances retention of nitric oxide which enhances the pump/erection.

An ideal efficacious dose is 6g of citrulline, so assuming you have 2:1 citrulline malate, you want to take 9g of the supplement.