yeah- if you're running on legitimate PSP hardware/Sony PSP emulation, 480x272 is the lcd resolution, although video out for the XMB on a 200X or later supports a larger resolution (strange). I had a lot of good luck utilizing a vga upscaler with zoom function, matching the vertical resolution, and allowing the hp lcd I was using to do a horizontal stretch on the output pixels. The best option for pixel accuracy on the 200X or later, however is to NOT zoom, and use a basic component to rgb/hdmi adapter. or one designed for the PSP I've started using an exploited VitaTV for fullscreen PSP gaming under CFW and it looks really nice. Now if you want actual image quality, if the game isn't too buggy under them, pc emulators like http://www.ppsspp.org look amazing because it won't impose the limited resolution of the PSP lcd.
Hmm... As defor and TriMesh had mentioned the screen made by either sharp (100x, 200x) or samsung (300x) is the odd 480x272 resolution. Games will be upscaled to 640x480 albeit letterboxed while umd movies will be the same as a DVD (720x480 w/ slightly more compression) TBH i'd just stick with those fixed resolutions. Its not great but its acceptable at best. You could also try playing PSP games on a PSTV. That or just emulate game w/ a phone (such as a galaxy s5 or a note 4), a tablet (Galaxy Tab pro or a Nexus 9) or a NVidia Shield hooked up to a TV and upscale it some how via the PPSSPP emulator on the Google play store.
You have PPSSPP but his emulation is far from accurate and compatibility list is not complete. Then you have PSP emulator in PSTV, it output 720P and 1080i, the quality is a bit bad but if you want to record from PSP it is the best option.
