Fahdk, The part number you would need is P9RN2, which is a component of the 0146H kit. You can also find a compatible one here as well. When you mix the dimm voltages, the 1.35v will just run at 1.5v dimms voltage. There won't be an issue mixing them, as long as the specs match. You can find more on the memory capabilities on page 71 here. Let me know if this helps.
I am planning to add some memory to a Dell T420 and trying to figure out the correct part number to order. The system shows as having shipped with both part numbers 0146H and P9RN2. This is under the Original Configuration for my service tag. But the system shipped with only 1x8GB ram module. What is the correct part number to order? Also, any issues with mixing 1.35v and 1.5v on this system? Thanks!
Dell T420 RAM - Part# 0146H or P9RN2?