Dell Precision tower T3620 add graphic card

You can put any card you want that will fit in the system.  The better question is why do you think you need a "standby" graphics card?  The failure rate for a graphics card is extremely low and replacement time would be the same as putting one in now and leaving it and not using it.  It would still be powered on so it would be just as likely to fail as the main card and you will not know if it is working or not, since you would not be using it.

I don't see any reason to use a second card if you don't need it for some other purpose.

Hi, thank for the reply but i think you had misunderstand what i mean.

i mean example the existing is 2GB graphic card so i add another one so that it will add up together and give me dual performance since changing 1 direct single high spec graphic card will cost more and wasted my existing graphic card.

Then if it was a clone PC then i know should be fine but since it was Dell so i was to double check were this machine able to slot another graphic card to add the performance. So any suggestion about that?

Do you have performance limitations with your P600? What is it you are trying to accomplish? What monitors and resolutions are you trying to output to?

As stated before, adding a 2nd graphics card will not help performance of the P600. It will still perform just the same, perhaps even a bit slower because of the added system overhead of commanding a 2nd GPU.

The previous post gives you details on SLI, which is an Nvidia technology that interfaces two, sometimes more, GPU's to share some workloads.  Are you looking to use SLI? What applications would you want to use SLI for? 

SLI support depends on the application. Windows and normal operations will not benefit at all from it.

I'm only adding that a 2nd graphics card also adds heat unless it vents out the back.