The head of the Federal Deposit Insurance Corp. said most banks don’t face excessive risks from their heavy investments in the government-sponsored enterprises, but he and other regulators pushed for better oversight of financial institutions. Last spring, the FDIC looked at the concentration of GSE debt at depository institutions, said Donald Powell, chairman of the agency, in a speech at this week’s annual convention of America’s Community Bankers in Washington. Firms insured by the FDIC…