A different address does not per se mean a different wallet, does it? Wallets always have several different addresses, right?
Yes. Wallets have multiple addresses. But why would I get a different address, then restore the file and get the same address as before? And for some wallets - including Jaxx - the address only changes when the old one gets used (receives a transaction).
What I'm gonna do now is let somebody look at it who knows more about PC's and crypto than me, and if that does not help then I will indeed submit a ticket there.
Submit the ticket already. There is a chance they will either tell you what is the issue and how to fix it, or at least how to get your private-key/seed from the Jaxx folder (or with any other method).