We are currently in Split and overall it's been a great trip, but we had a very stressful experience involving the ferry from Vela Luka (Korčula Island). We went to the Jadrolinija office in Korčula town on Thurs to buy tickets. The agent there told us not to buy them; she gave us some rap about needing to be in line really early to guarantee a space and having a ticket would not do so.
So we got there super early, and, lo and behold, there was a power outage on the entire island, which we were not aware of when we left Lumbarda. We did not have the cash, ATM's were down, so we were not able to buy a ticket.
I had to give the ferry manager my passport to be let aboard and he told me that I would buy the tickets at the office at the Split ferry terminal and they would return my passport there. Got to the office, met our AirBnb host, found parking, waited in line, and the agent did not have it. They tried calling the ship but no answer. Finally, an employee went to the ship herself and retrieved my passport. I got it with about 10 minutes to spare before the ship was to leave on its next journey.
It ended well but it was a very nerve-wracking, stressful experience.
So my suggestion is, buy your tickets in advance if at all possible, no matter what the agents may say. Or otherwise make sure you have enough cash on hand. You never know if a power outage might gum up the works.
PS: There were not many cars on the ferry and it wasn't necessary to get there almost three hours early.