Dynegy Inc. would sue to stop power purchase agreements for Ohio electric utilities if state regulators approve the controversial proposals. The plans would allow the utilities to buy electricity from their affiliated power plants via long-term contracts and sell it on the open power market. It would mark a return to regulation for that portion of power and a major shift under Ohio’s deregulated power market. Risk would shift to ratepayers instead of the companies and their investors. The utilities project customers would ultimately benefit, while opponents say the proposals would cost customers.