There isn't really a difference. Jupiter Optimus Maximus (literally Jupiter the Best and Greatest) was the top god of the Roman pantheon, whose temple was on the Capitoline Hill - hence 'Capitolinus', which means 'of the Capitoline.' Construction of that temple had supposedly been started by the last Etruscan king, before the Romans ran him out of town. One of the first things the young Republic did was finish the temple, so it had connections deep in Roman history. From then on, 'Capitolinus' was pretty much synonymous with 'Optimus Maximus' as names for Jupiter, even outside the city of Rome. There are dozens of inscriptions dedicated to either Jupiter Optimus Maximus, Jupiter Capitolinus or even Jupiter Optimus Maximus Capitolinus all across the empire, making it pretty clear that people didn't really recognise a clear distinction.