you can upgrade cpu and ram, but bear in mind the limit of this model because it is on LGA775 platform.  spending about same amount of money to get a Optiplex 790 will put you on intel Core i5/i7 LGA1155 platform, 25-30% faster speed etc. having said that, in general ram of desktop only pc3-12800 or ddr3-1600 are good.  choose a name brand such as hynix micron samsung. no need to be concerned about detailed ram latency at this stage. you cannot officially upgrade DT psu due to its oem nonstandard form factor, that is another limit.  [IMAGE] a low profile gpu that is single slot width and not too long may fit DT.[IMAGE] 4x4 gb works for 780 as validated by user benchmark.  Q9650 costs around $40-50, not really great for this model.  you could have spent that on ssd.
I have decided to upgrade my OptiPlex 780 DT I have Dell OptiPlex 780 DT with Motherboard Dell Inc. 0200DY, Core 2 Duo E8500, (HDD 250 GB 7200RPM) Hitachi HDS721025CLA382 , RAM M378B5673FH0 - CH9 (2GB 2Rx8 PC3-10600U - 09 - 10 -B0) , PSU(Power Supply Unit) Model D255P- 00 REF.NO:DPS-255BB (255W).No any GPU I have on it. [IMAGE] [IMAGE][IMAGE] I am getting issue with the speed. I'm thinking of buying Core 2 Quad Q9650 and GPU 512MB ATI RADEON HD 4550. I have seen somewhere that Core 2 Quad Q9650 have the RAM capacity of 4x4gb(16gb) but My Motherboard is showing Only 8GB of RAM capacity "MaxCapacity = 8388608 so I'm in doubt of which RAM should I buy?  What could be the best RAM(with max memory bandwidth speed, CL(Cas Latency), Data Rate & everything on it? [IMAGE] and also have doubt in 'Will Core 2 Quad Q9650, GPU 512MB ATI RADEON HD 4550 and 4x4GB(16GB)RAM work on PSU 255W or should I have to upgrade PSU 255W as well? If yes then How should I Upgrade my PSU & to what Watts?? Am I doing the Best Upgrade or not?? Or Kindly Suggest me What could be the Best Upgrade? I'm in hurry to Upgrade My PC as soon as possible Kindly Reply me simple & straightforward ASAP with links as well...
Dell Optiplex 780 DT upgrade issue