Originally designed for MAME (Multiple Arcade Machine Emulator) to compress CD-ROMs from the Sega CD and PlayStation 1, CHD has recently been adopted by PPSSPP (the leading PSP emulator) and modern handhelds like the Steam Deck and Anbernic devices.
Look for collections uploaded by users like RetroRoms or Vimm’s Lair (mirror). The best sets include a .dat file for RomVault.
Unlike CD-based games, PSP games must be compressed using the with a specific hunk size for best performance in PPSSPP. Easily Convert PSP ISO To CHD For PPSSPP