It certainly looks like it. Of course, it's not impossible that the wiring is different, but the connector looks the same. The physical unit looks about the size of a normal ATX power supply too, but you'd need to make sure the AC input/output and fan matches up with the cutouts on the case (Assuming you're using an original Power Mac tower)
As keropi says, a piccy is worth a thousand words, so here's three:
That was the plan, but I couldn't make it boot MorphOS 2.4 -- It is supposed to work with Mac Minis, but nothing has been said about Power Mac G4 towers though. Still, there's always MorphOS 2.5 to come!