RX580 is just RX580, all RX580 chips are from AMD with device ID 67DF.
Power Color is the brand name of the graphic card that use the AMD chip. Just like Sapphire, MSI, XFX, etc.
In general, brand name doesn't matter. As long as that's a RX580, the cMP can use it (at least true in High Sierra).
However, in reality, this is only true for the reference card. For highly custmoised card, they may be shipped with a highly customised firmware that has compatibility issue on the cMP. Even the chance is low, the it's not zero.
So, I bet the Power Color RX580 95% can work normally on the cMP.
Anyway, for "supported", the answer is no. Most likely they can work flawlessly, but never really supported by Apple. The supported garphic cards list is here
Learn which built-in and aftermarket graphics cards work with Final Cut Pro, Motion, and Compressor on Mac.
support.apple.com
You can see that Sapphire PULSE RX580 is supported, but they didn't mention the Power Color RX580. Which means, not supported.