I went to the PB website, and couldn't find any model 5069, but the imedia 5096 looks like a pretty standard format ATX-style mini-tower (but I couldn't see the PSU area, so I could be wrong). So, "IF" it's a standard ATX power supply, I would suggest a 400w one from OCZ, Enermax, Fortron Source, Sparkle, Antec (the TruePower series), or a couple others. Depends on whats available in your area.
I would still check and see what brand and rating the PSU in the system is - if it's already a pretty powerful system (the 5096 is a P4@2.66ghz, so that's not a slouch), the PSU may be decent. (though I wouldn't hold my breath, I'ld still look into it.)