I was referring to all three: Discover, JCB, and UnionPay. None of these three supports DCC. Only Visa and MC support DCC.

I went into detail about UnionPay because they do have a spread on their exchange rates that's a little higher than Visa/MC. The limitations on using one of these cards are the acceptance as well as few card products available/limited rewards compared to Visa or MC products.

The ICBC UnionPay is a viable alternative in places like Hong Kong, Macau, and Mainland China, especially in unavoidable DCC cases for 1x merchants.