Specific for the oxidation of the 20-alpha hydroxy group of 17-alpha-hydroxyprogesterone and 17-alpha-hydroxypregnenolone. (17R,20S)-17,20-dihydroxypregn-4-en-3-one + NADP(+) = 17alpha-hydroxyprogesterone + H(+) + NADPH (17R,20S)-17,20-dihydroxypregn-4-en-3-one + NAD(+) = 17alpha-hydroxyprogesterone + H(+) + NADH Homodimer.