Catalyzes the NADP(+)-dependent oxidation of succinate semialdehyde to succinate (PubMed:20174634). Thereby functions in a GABA degradation pathway that allows some E.coli strains to utilize GABA as a nitrogen source for growth (PubMed:7011797). Also catalyzes the conversion of glutarate semialdehyde to glutarate, as part of a L-lysine degradation pathway that proceeds via cadaverine, glutarate and L-2-hydroxyglutarate (PubMed:30498244). H2O + NADP(+) + succinate semialdehyde = 2 H(+) + NADPH + succinate 5-oxopentanoate + H2O + NADP(+) = glutarate + 2 H(+) + NADPH The succinate-semialdehyde dehydrogenase activity measured in the presence of NADP(+) is approximately 20-fold higher than that measured in the presence of NAD(+). Amino-acid degradation; 4-aminobutanoate degradation. Amino-acid degradation. Homotetramer. Induced by RpoS in response to multiple stress conditions, including shifts to acidic pH, nitrogen limitation or high osmolarity as well as starvation or stationary phase (PubMed:14731280). Induced by gamma-aminobutyrate (GABA) (PubMed:7011797). Belongs to the aldehyde dehydrogenase family.