2GB RAM Memory for Dell OptiPlex 780 (Performance Mini Tower ) 240pin PC3-8500 DDR3 DIMM 1066MHz Black Diamond Memory Module Upgrade - Walmart.com
780 DT, GPU and RAM upgrade help? - Dell Community
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 2X2GB RAM Memory for Dell OptiPlex 780 (Ultra Small Form Factor ) DDR3 DIMM 240pin PC3-8500 1066MHz Black Diamond Memory Module Upgrade System Specific Memory - Newegg.com
Optiplex 780 - Dell Community
CMS 8GB (2X4GB) DDR3 10600 1333MHZ Non ECC DIMM Memory Ram Upgrade Compatible with Dell® Optiplex 780 Dt/Mt/Sff Desktops - A69 at Amazon.com