Pretty much every national chain, especially supermarkets, accepts credit cards. You won't have as much luck at owner-operated stores or restaurants. Berlin is probably the most card-friendly place in Germany by the way.

I'm indeed thinking independent stores, family-run restaurants and discount markets such as Netto which only accept the German card; local kiosks and fast-food places take cash only. I can confirm credit card works in upscale markets (like Rewe) and major chains.

Both Netto with and without a dog in the logo (competing chains with the same name) now accept credit cards, same with other discount markets such as Aldi, Lidl, and Kaufland. Major exceptions in the food sector are most Penny and many Edeka stores (a lot of the latter I would categorize as "upscale"). You are right about independent stores and restaurants. Unless you know for sure all places you plan to go to take cards you should carry enough cash.

> both Netto with and without a dog in the logo

I call them "red Netto" and "black Netto" because of the yellow-red and yellow-black color scheme. (The main color is, frustratingly, also the same.)