Even PBS has ads nowadays. At the beginning of a show, "sesame street was brought to you today by support from viewers like you, and..." (ad for abcmouse, some minivan, etc plays)
No, it used to be where they would mention the name of the company on a still image and a quick blurb, like the other poster's youtube link. Now the company gets a whole 30 second ad like any other channel.
That’s how public broadcasting works in the US. A number of other countries manage to have public broadcasting without any private advertisements or sponsorship. (For example, Australia’s ABC.)