Convert PPSSPP save data to PSX?

[LunaMoo]

If by "PSX to PSP" you mean you want to repack a game from psx to psp then forget about it. PPSSPP(as well as other psp emulators) supports only real PSP eboot.pbp files. PS X/One games will never be supported as was said many times because psp was also unable to run those games natively and ran those games over an emulator ~ writing another emulator inside ppsspp just has no sense even less with soo many already existing.

Not really sure why are you mentioning Suikoden 3 here through since that was a ps2 game, meaning it has nothing to do with ppsspp.

If you do want to run proper PSP suikoden games, they're updated japanese versions remade for psp so it's very unlikely for PSOne saves to be in any way usable in it, besides those versions were fixed and improved, so it's completely worth playing from 0.