I have two blackbirds with PPC cards. The one is apple official, the other is Nupower. 

The nupower one is unstable at best. crash/bombs, etc.. After it warms up its fine. (not caps, various logic boards and PS adapters, all do the same thing). 

Then the apple official one works great. Even has the PowerPC emblem on top of the bezel. I found it dirt cheap on ebay, it flew under the radar a few months back. 

Since I got nothing to lose, I was going to drop a 200mhz PPC chip onto the nupower card and see how that worked. I got an IBM CPU card that has a 200mhz 603e.