The vast minority of utilities in the United States, by number of customers served, are investor-owned; publicly-owned and co-operative utilities only cover 50m people.[1]
Theoretically, the grid is supervised by the California Public Utilities Commission, which has wide latitude to set standards and regulations for PG&E and others. The Public Utility Code is the highest law in the state of California[2], so IMHO a large part of the blame for PG&E's failures fall on CPUC's failed oversight[3][4]