My friend bought a Dell computer a few months ago, the XPS 8500. It came with 16GB of RAM, but because he does work on this computer he needs 16GB. He would like to save money and just get another 8GB instead of buying a whole new set of 16GB. Since it was prebuild he doesn't know the brand of memory that he has, so does he need to match the brand, model, CAS, and/or speed of the RAM?