I own a PowerMac G5 that originally was fitted with a nVidia GeForce 5500 AGP 64MB GFX card, but as this is not compatible with MorphOS I needed a GFX card that was. So I acquired a Radeon 9200 128MB PCI card and fitted that in the next lower (PCI) slot in the G5 board.

I had to connect the video monitor to the connector on the Radeon PCI slot to use the card, but MorphOS was viewable on it, even though I seem to remember the nVidia card was still sitting in the AGP slot. It's a while ago, but that's the basics of how I used a Radeon 9200 PCI card in my PowerMac G5, though I've since located an Apple/Mac based Radeon 9600 128MB AGP card so the 9200 is no longer required for the moment for that purpose.

My use of the Radeon 9200 was extremely brief, it was more to test the PowerMac G5 hardware itsef, as it had a faulty CPU when I got it, and I had to replace it, so that required re-installation via Mac diagnostic software to get the fans to run at an acceptably quiet/slower speed, instead of on full speed all the time - requiring calibration.

So, a Radeon 9200 PCI card is useable with a PowerMac G5, and I believe it is also OK with a G4 PowerMac, but other hardware I am unsure if there are PCI slots compatible in other hardware with that kind of card.