It's always best to get a single kit of RAM (ie, a single kit of 4 identical modules) so that there is less chance of having compatibility problems, even if the modules have the same part number, the chips all have the same part numbers, etc. There is always a chance of compatibility problems when etch runs are different, when the timing chips are different, when the capacitors or resistors have different tolerances, etc.
What speed are you running the RAM sticks at? "Overclocked"? If overclocked try standard speed, DDR4 2133.
Hopefully you don't have a bad RAM slot. Make sure you reseat the RAM modules after pulling the AC cord - maybe it's a seating problem. If it has been months since the RAM was first installed you may have dust in a RAM slot so blow it out with canned air (don't continue to use the can if it starts getting cold - only use if the can feels normal). In a pinch an hair blower will work, provided that it is not on a heat setting.
The first thing to do is, after pulling the AC cord, is to see if the two new modules work in place of the two RAM sticks already installed in the PC. Run a few passes of MemTest86 on all four chips after re-connecting the AC cord.
And as always, never touch any etches, any chip or any gold fingers on RAM. Clasp the stick lengthwise and push down on other ends at the same time to seat properly.
