The brand of the RAM is completely insignificant since you really only have about 3 companies making the actual DRAM chips. What you want is for all of the various specs to line up as closely as possible. So if you have DDR3-1600 CL9 3-6-3 (numbers are fictional and for the sake of example only) modules now, then the ideal would be to find more DDR3-1600 CL9 3-6-3 RAM. If you can't find anything that matches what you have now exactly, then the smaller the variance the better.
It takes time for my vendor to RMA, that's why I just plan to get a new stick instead of waiting.
Can I purchase another 2GB x2 Vegeance and use the remaining 2GB x4 to run Triple Channel ?
Do they need to be in the exactly same stock type(1600), latency(9-9-9-24) and voltage(1.5v) ? or just the same voltage will do ?