Catalyzes the NADP(+)-dependent oxidation of succinate semialdehyde to succinate. It is believed to be the main source of succinate semialdehyde dehydrogenase activity in Mycobacterium. NAD(+) can substitute for NADP(+), but enzymatic activity is three times reduced. H2O + NADP(+) + succinate semialdehyde = 2 H(+) + NADPH + succinate Belongs to the aldehyde dehydrogenase family. Extended N-terminus.