Do publicly-owned utilities already exist?

Yes. There are publicly-owned utilities all over the country, among them are the utilities for Los Angeles and Austin. The state of Nebraska has zero investor-owned utilities. The most famous public power corporation at the federal level is the Tennessee Valley Authority, created by Franklin D. Roosevelt when he was President. A more recent example is in Massena, New York, where residents voted to municipalize their investor-owned utility in the 70s, and today they pay some of the cheapest prices for some of the cleanest energy in the state. They pay 4 cents per kWh/hr, with all charges included, compared to 15 cents per KWh/hr that their neighbors in National Grid territory pay.

On the supply and transmission side, an extremely successful and financially lucrative example is the New York Power Authority, created by the state legislature under Governor Roosevelt in 1931. To date, NYPA holds high bond ratings, provides some of the cheapest energy in the state, and continues to lead the way for affordable renewable energy.