Super U definitely accepts credit cards. They are unfortunately no longer accepting 1 to 1 on the dollar, but their prices are definitely the best. I haven't seen any reports on Simply in the past couple of weeks, but prior to that, all reports were very bad.

Super U is in Marigot, where Match used to be, if you're a long timer. Simply is in Hope Estate, close to the roundabout that goes to French Cul de Sac.