I have Super Street Fighter IV on disk. US. My PS3 is US.
Ultra SSFIV is on sale on the Japanese PSN store for 750 yen. I have a Japanese PSN account and have bought stuff from there in the past.
Question is, can I use the Japan-store purchased Ultra to upgrade my US bought SSFIV?
Good luck with that - Sony refunds money only in cases of corrupted files etc. They have information about game versions which work with the selected DLC so according to the EULA you accepted, you don’t have rights to the refund. There was a case in a past week about a guy who got his account stolen and had some game bought on another console using his saved credit card information, Sony acknowledged this, but still said "Fuck you no refund kthxbai"