There are four parts to Medicare. Each represents different coverage. Part A is hospital insurance. Part B is medical insurance and Part D is prescription drug insurance. The Medicare Part C definition is mixed.
Medicare Part C is at the very minimum, the same as part A and B. The difference is that Medicare administers A and B. With part C, a private insurance company provides the coverage and is paid back by Medicare. The advantage of Part C is that an insurance company can expand on the benefits beyond what Medicare provides.
A Medicare supplement plan is purchase in addition to Medicare. You can only get a supplement plan if you have Medicare Part A and B. There are coverage gaps in Medicare. You may end up with a large out-of-pocket expense after a covered medical event. The purpose of Medicare supplement policies is to fill these gaps. There is a fixed number of specific supplement plans available, each with a different combination of coverage. You can choose one that fits your needs.
As stated earlier, a Medicare Part C plan must have at least the same coverage as Medicare A and B. If it only provides minimum coverage, you might incur the same out-of-pocket costs if you chose Medicare. You cannot add a Medicare supplement plan to a Part C plan, so it is important to choose a part C plan that includes your needed supplemental coverage.
Another advantage of Part C is that the plan may offer coverage beyond what the supplement provides. For instance, a plan may have coverage for hearing or vision.
In the end, your choice is either Part C or a combination for Part A, B and supplement insurance. It is an either or choice. Be sure to check the details and total cost of the plans when you compare them.