CMS 32GB (2x16GB) DDR4 19200 2400MHZ Non ECC SODIMM Memory Ram Upgrade Compatible with Dell® Latitude 15 (5580), Latitude 15 (5590), Latitude 15 (E5570) - C108 at Amazon.com
Dell Refurbished Latitude 5580 15.6" Laptop Intel Core i5 16GB Memory 512GB Solid State Drive BB5-32865 - Best Buy
How to replace the Memory in your Dell LATITUDE 5580 | Dell US