well...i have never tried DVDfab
But if you wanna put DVDs on your PSP, might i give you a suggestion?
I use
DVD Decrypter
Then
Videora iPod Converter - Free iPod Video Converter
while converting, you can increase the quality in one of the last steps. Use this guide:
DVD to iPod Video Converter Guide
I put Blue Harvest on my PSP this way, it was compressed down to 356MB!!! And the quality was Amazing!
EDIT: oh, and even though it's an ipod converter, it works just great for PSP.