I used my CSP and Citi Premier in all sorts of restaurants. Usually for Shanghai, they either accept all kinds of credit cards, or they are cash only. For the restaurants that Americans would go to, I would say Visa/MC are widely accepted.

Using Discover at UnionPay-only places can always generate understanding problems, so be aware, even though any place accepting UnionPay technically can swipe Discover.

BTW, most of the terminals in Shanghai are as I guess direct-linked to UnionPay, and I also guess that UnionPay handles the gateway to Visa/MC networks. Therefore I don't see a lot of DCCs there, since DCCs usually happen with terminals supplied by the banks. You always see "银联商务" on receipts printed in Shanghai, but in Beijing you usually see logos of the banks like BoC, CCB, ICBC (ICBC ones are hard-DCC free though), and etc.