I’m no expert here, but AFAIK it is possible for a power amp to damage speakers if it outputs too much DC.
As for the Supercap, I think it would be very unlikely that it might damage another piece of kit. However, I have heard of equipment with switch mode supplies going bad and frying other connected equipment. In fact I recall a very unhappy customer once sending in their Naim system because it all got fried twice. Initially both the customer and the dealer were adamant that it was fault with the Naim kit. We couldn’t figure out how it was possible. So we asked for to borrow their very expensive source component to see if that had anything to do with it. The source component used a switch mode power supply. After a few days running we noticed that it was somehow sending a massive power spike through the rest of the system. We had found the culprit. Much humble pie followed…