There is Schwyzerdütsch (sp?) - and there is German with a Swiss accent.

The former is a dialect according to some, and a separate language according to others. It is as different from German as Dutch or Letzeburgisch (the language of Luxembourg). It's what Swiss people speak among themselves in informal situations.

German is the language of education, it is the language used in written communications, and until a couple of decades ago it was the only language used on TV and radio (there are now some stations that broadcast in Schwyzerdütsch).

There may still be some old people in some remote mountain villages that only speak Schwyzerdütsch, but as a general rule Swiss people can speak standard German and will switch to standard German the moment they realise that the other person is not Swiss. A Swiss speaking standard German is as intelligible to a German as an American speaking standard American English is to a British person.