How do I list all available encoding types available in postgreSQL?
Or are the only encoding types ever available listed in Chapter 23.3 Character Set Support?


Yes. You can see the full list in the source code, if you insist

That said, it's highly abnormal to use any of these encoding except UTF-8 as an internal storage format. Unicode should support all of the useful characters in all of the other encodings. If you find UTF-8 acceptable, the only purpose these other encoding serve is to eliminate the need to create an ETL script for the COPY statement.