Catalyzes the NADPH-dependent reduction of 2,5-diketo-D-gluconate (25DKG) to 5-keto-D-gluconate (5KDG), 2-keto-D-gluconate (2KDG) to D-gluconate, and 2-keto-L-gulonate (2KLG) to L-idonate (IA). D-gluconate + NADP(+) = 2-dehydro-D-gluconate + H(+) + NADPH Belongs to the D-isomer specific 2-hydroxyacid dehydrogenase family.