OFFTEK 4GB Replacement Memory RAM Upgrade for Dell OptiPlex 390 (Desktop) (DDR3-10600 - Non-ECC) Desktop Memory at Amazon.com
Dell Optiplex 390 MT Intel Core i3-2100, 4GB RAM, 120GB SSD, Windows 10 Pro | eBay
Amazon.com: Dell Optiplex 390 Tower Business High Performance Desktop Computer PC Wi-Fi (Intel Quad-Core i5-2400 up to 3.4GHz, 8GB DDR3 Memory, 2TB HDD, DVD, Windows 10 Pro 64-bit HDMI (Renewedd) : Electronics