according to the on hand info from AARP it says that plan N is a 20 dollar co-pay for doctor visits.
The term used “excessive charges” applies to a situation where a doctor would charge over and above the medicare eligible amount allowed.
As I recall from a meeting with a rep it depends on which state you receive the care. For example, it could happen in the state of Florida. Medical providers in other states (OH is one) that do not allow providers to charge above the medicare eligible amount.
I have Aetna Plan F and as I need injections for wet macular degeneration I am very grateful for this outstanding coverage. I have never made a co-pay so far.
By the way, I did not know I would have wet macular degeneration but it happened the same month my coverage started.