Where can I find open GIS/location data on coal power plants?
Existing Electric Generating Units in the United States (you would also need to find the retired plants that are no longer licensed). However, this doesn’t really tell you about the living dead ones that are rarely turned on, so you would want to look at actual fuel usage. FERC Form 423 has the actual use and quality of fuel. There are a few companies that aggregate EIA/FERC/etc data, but Platts is the one that I know does stuff with maps.
There is a comprehensive list of power plants from 2000 here; some poking around on the DOE website may get you additional/more recent info.