I have loads knocking around for projects and stuff, but I have a lot of other hardware anyway, so I generally just use a Core Grafx/Supergrafx.
Also, an extra volt is well above tolerance for the PCE (it actually gets converted down to 5v internally, and the part that converts is rated to like 20v). I mean get an extra one anyway, but even if you tested the output, it probably wouldn't be exactly 9v. Just to set your mind at ease
PC Engines are tough little things!