The PRX format contains lots of debug information as its basically a library. Some games implement some major parts of the game logic in prx files rather than in the EBOOT executables.
sym files but are created by the linker to document where each function is located in the final linked executable. SYM Files are generated by the SN Systems ProDG SDK for PSP for use in debugging, they contain all the symbols (function names etc) and can also contain other chunks such as source filenames and line numbers. Types of PSP Symbol files SYM Symbol Files Some games also ship with unencrypted executables in BOOT.BIN The Sony Playstation portable used encrypted executables known as EBOOT.BIN, these are basically just an encrypted ELF file and it is possible to decrypt them with the correct tools.
Playstation Portable Games with Debug Symbols Edit on Github