Catalyzes the NADPH-dependent reduction of trans-2-enoyl thioesters in mitochondrial fatty acid synthesis (fatty acid synthesis type II) (PubMed:12654921). Fatty acid chain elongation in mitochondria uses acyl carrier protein (ACP) as an acyl group carrier, but the enzyme accepts both ACP and CoA thioesters as substrates in vitro. Displays a preference for medium-chain over short- and long-chain substrates (By similarity). May provide the octanoyl chain used for lipoic acid biosynthesis, regulating protein lipoylation and mitochondrial respiratory activity particularly in Purkinje cells (By similarity). a 2,3-saturated acyl-[ACP] + NADP(+) = a (2E)-enoyl-[ACP] + H(+) + NADPH (2E)-butenoyl-[ACP] + H(+) + NADPH = butanoyl-[ACP] + NADP(+) (2E)-hexenoyl-[ACP] + H(+) + NADPH = hexanoyl-[ACP] + NADP(+) (2E)-octenoyl-[ACP] + H(+) + NADPH = NADP(+) + octanoyl-[ACP] (2E)-decenoyl-[ACP] + H(+) + NADPH = decanoyl-[ACP] + NADP(+) (2E)-dodecenoyl-[ACP] + H(+) + NADPH = dodecanoyl-[ACP] + NADP(+) (2E)-tetradecenoyl-[ACP] + H(+) + NADPH = NADP(+) + tetradecanoyl-[ACP] (2E)-hexadecenoyl-[ACP] + H(+) + NADPH = hexadecanoyl-[ACP] + NADP(+) Homodimer. Belongs to the zinc-containing alcohol dehydrogenase family. Quinone oxidoreductase subfamily.