You can mix RAM brands, but you probably shouldn't.

Usually. But “usually” is carrying a lot of weight here.

Mixing brands means two different sets of sticks with potentially different timings, voltages, and chip quality. Modern motherboards and CPUs are pretty good at figuring it out—they’ll default to the slowest common speed and timings. So it’ll boot and work. Often.

The problem is stability. You might get random crashes, blue screens, or weird performance hiccups that are a nightmare to diagnose. The money you save buying a mismatched kit is rarely worth the headache. A single matched 32GB kit (2x16GB) is tested to work together, usually costs only a little more, and you get peace of mind.

If you already have one stick and want to add another of the same specs from a different brand, go ahead and try it. Just keep the box for the new one in case you need to return it.

Better to sell your old RAM and buy a single matched kit. Future you will thank present you.