Match the stick if you can find one.

Probably, but only if you buy the exact same model. DDR5 is picky about mixing sticks—different brands or even same brand different revision can cause instability or force the memory controller to play it safe at slower speeds.

If you can find the identical 8GB stick (same part number, same timings, same voltage), then grab it. Your i5-12400 will run them in dual-channel just fine. If you have to guess or buy a generic “DDR5-4800” from another brand, don’t. The risk of losing performance or getting random crashes isn’t worth the $30 you’ll save.

A 2x8GB kit guarantees the sticks are matched from the factory. That’s the safe route. You can sell your old stick for maybe $20 and offset the cost.