I use a PZ40X (or equivalent) with my Nikon dSLR and frankly the
on-camera flash is better. The Sunpak always badly underexposes even
thought it is using iTTL connection. I have never had any complaint with
Sunpak on film cameras.

Does the G9 not have an on-board flash? If you are looking to use
something else then look at a small hammer-head flash as it has the
advantage that it can be held away from the camera or even used more
effectively than a hot-shoe flash for bounce flash.