Small quibble here. I'm pretty sure that most regulated companies do NOT own their own generating plants, since for a long time they were legally not allowed to be in both the distribution business and the generator business. I _think_ this was from the Public Utility Holding Company Act (https://en.wikipedia.org/wiki/Public_Utility_Holding_Company...) but it was ~ 15 years ago when I toured an Entergy power plant and heard the explanation so I may be wrong. I suspect that this still holds true for regulated utilities since the conflict of interest is pretty high.

What has been a recent trend is generator companies purchasing supplier companies (for example Calpine purchased Champion Energy and Noble Solutions)