I am not certain but I believe Carnival Corporation has been using Fincantieri as the almost exclusive builder of their ships for a while now.
And yes, out of economic and production reasons they would use the same or similar designs for the propulsion and electrical distribution systems between classes of ships. This is not unusual. I know the U.S. Navy has done it for decades, especially in nuclear powered ships, which is what I did, but also in having common layouts for conventional steam propulsion plants, as well as those of the diesel and gas turbine ships. Plus this reduces training time and costs since an engineering officer or seaman can go to different ships and already be qualified to operate the equipment.