27 inch iMac ram upgrade question.
I am expecting a new 27 inch iMac tomorrow, and I plan on upgrading the ram. I have watched the videos on how to upgrade the ram; and in some videos they mix the existing Apple ram and the new ram. I am transitioning from the PC world and I would like to know if this is a common practice. I plan on installing 16 gig Corsair Vengeance ram, which is supported by Apple in the 2017 27 inch iMac. Should I mix the ram, or only use the Corsair Vengeance ram? Any and all replies are greatly appreciated from a Mac newbie.
iMac