Medicare Supplement Plan C is one of the strongest Medicare Supplement plans or Medigap policies that provides coverage for almost all of the coinsurance and copayment requirements of Original Medicare. It lacks only one benefit, and that is coverage against Part B Excess Charges. While excess charges are rare, some states allow physicians to charge up to 15% more than Medicare would normally cover for a given service. Medicare's term for what they consider usual and customary is known as Medicare assignment. A physician may accept Medicare, but not accept Medicare assignment and therefore reserves the right to charge you an additional 15%.