Nice buy !!
GPD XD is the perfect portable console for PSX , SNES ,MD,NEC,MSX etc etc .... the emulation is perfect. You will need to try some configuration for find your perfection and the last version of each emulator is recommended.
About PSX , i was using the last verion of EPSXE , very good emulator with a lot of options but in fact, even setting in " lowest latency experimental " options , there is a little lag with the action and the sound. Like 0.4 sec maybe ?
So , recently I prefer to use the last version of FPSE , there is no sound lag or if is : ( very unnoticeable ) and the graphic render is like original PS1.The bad point of this emu is that sometimes there is some veeeerry little ( close to unnoticeable ) crack sounds .... well , both PSX emulator are fantastic !
Wich games do you want to run on PSX ?or other emulator ?