Originally Posted by
photaco
Not online, not really. I've never heard of a merchant outside a Discover-issuing country that accepts Discover online. JCB and UnionPay online merchants aren't compatible with Discover, and the same is probably true of Diners Club (especially in Japan and mainland China, where Discover isn't even compatible with Diners Club physical merchants)
I just tested this and can thankfully confirm it is untrue and it does work online in Diner's Club countries. I had to make a £21.50 purchase with our student union, which accepts Visa, MasterCard, and JCB, and Diner's Club.
I decided to try my Discover, picking Diner's Club for the card type from the drop-down. It went straight through, and the pending amount on my online account is $31.33 which is about 0.2% worse than the spot rate according to Google. That's as good as FX gets in my experience. Now, I'll lose some converting my pounds to dollars as ultimately I'll need to I don't earn dollars anymore, but the Discover rewards will mostly offset that. A worthy experiment, I dare say.