Catalyzes the reduction of 3'-oxosphinganine (3- ketodihydrosphingosine/KDS) to sphinganine (dihydrosphingosine/DHS), the second step of de novo sphingolipid biosynthesis. {ECO:0000269|PubMed:19141869, ECO:0000269|PubMed:28575652, ECO:0000269|PubMed:28774589, ECO:0000269|PubMed:34373586, ECO:0000269|PubMed:36170811}. This is the function of Ensembl gene identifier ENSG00000119537 (KDSR, 3-ketodihydrosphingosine reductase).