There were no capitals for medieval (Latin) Christian kingdoms as such, esp. for kingdoms the size of Germany, where the monarch had to be itinerant. The "capital" is a modern concept, although strong, highly centralized monarchies like Visigothic Spain, the Caliphates, the early Roman Empire and the "Byzantine" Empire had the infrastructures and state cultures to make what we would call a "capital" possible. But wherever feudal ties have been more important than bureacratic infrastructures, then "capitals" have been irrelevant.There were, though, ancient coronation centers, congregation points, dynastic strongholds and palaces. For the typical Holy Roman Emperor, he'd be crowned as king of the Germans/East Franks at Aachen, King of Italy/the Lombards at Pavia, King of Burgundy at Arles, and king of the Romans at Rome. (Likewise, Kiev in Russia, Toledo in Spain, Rheims in France, Scone in Scotland, Tara in Ireland, etc ). Congregation points for the German princes and High Clergy included Worms, Constance, Augsburg and Regensburg among other places. Locations of a palace or stronghold varied according to ruler or dynasty. For the Otto III, if I remember correctly, brought up by a Byzantine princess, his residence was mainly in Rome...although his dynastic power-base was in Saxony. Otto III though, was a peculiar example of a German king who ruled at a time when his realm enjoyed a greater deal of centralization than probably any other Latin monarchy. He had tried to make Rome his "capital", but died tragically young.
Compare with the rulers of High medieval England. They spent most of their time in France, where, like the German kings in Italy, they had more important interests...which is why Rouen was more important to them than London or York.