8GB Kit (2 X 4GB) DDR3 Memory Upgrade for Dell OptiPlex 780 Small Form Factor Desktop PC PC3-12800 240 pin 1600MHz RAM (PARTS-QUICK Brand) at Amazon.com
4GB RAM Memory Upgrade for the Dell Optiplex 780 Mini Tower | eBay
780 SFF, ram upgrade - Dell Community
4GB 2X2GB RAM Memory for Dell OptiPlex 780 (Ultra Small Form Factor ) DDR3 DIMM 240pin PC3-8500 1066MHz Black Diamond Memory Module Upgrade - Newegg.com