At the initial standardization period there were a number of Unicode transport protocols, some of them really weird (7-bit UTF for one). As of now Notepad++ is pretty straightforward with what needed. It has in its settings:
- UTF-8 (default, plus switch "Apply to open ANSI files")
- UTF-8 with BOM
- UCS-2 Big Endian with BOM
- UCS-2 Little Endian with BOM
- other (long-long list)
The rule of thumb is that default UTF-8 + "Apply to open ANSI files" is the only thing one ought to use.
Anything else is only for two distinct situations: 1) one got some unreadable chunk of chars from a 3rd party file and needs to make it readable Unicode 2) one is seeking for new oops-type adventures for (her|him)self and for end users.