Required for branched chain fatty acid synthesis. Catalyzes the reduction of the 3-ketoacyl-CoA intermediate that is formed in each cycle of fatty acid elongation. Very long-chain fatty acids (VLCFAs) serve as precursors for ceramide and sphingolipids. May also be required for sterol hormone production (By similarity). a very-long-chain (3R)-3-hydroxyacyl-CoA + NADP(+) = a very-long-chain 3-oxoacyl-CoA + H(+) + NADPH Lipid metabolism; fatty acid biosynthesis. Belongs to the short-chain dehydrogenases/reductases (SDR) family. 17-beta-HSD 3 subfamily.