We have just traversed this path with a 230/240V, 50Hz boat. The most common, but by no means universal connector was this one (IEC 60309):
This type comes in two sizes, the most common is 16A, the next size up can sometimes be found, but most systems across the Pacific can't provide the large quantities of juice you may be accustomed to. These connectors are almost universal in former European possessions, especially French.
When you get to NZ the system is different, and at least in theory your shore power cord and connections must be inspected and labeled by a local licensed electrician. Some marinas enforce this more than others, but there are people who walk the docks checking the certification
labels on the cords. Best bet is to find a friendly marina on arrival where you can get your cord certified inexpensively, then the label is good for a year at more strict places.
We never tied up in Tonga/Fiji/Cooks so didn't really look at them there.
As the others have said, you will likely end up in the hardware store several times and swapping the plug at the shore end of your cable as you get to different places.