Match the specs, not the brand.

Probably. As long as the new stick has the same capacity, same speed (MHz), and same timings (CL), brand doesn’t matter much. The system will run them both at the slower stick’s speed anyway, so don’t buy a faster stick thinking you’ll upgrade—you won’t.

Where it gets dicey: different voltage or different ranks (single vs dual). Most modern DDR4/DDR5 sticks are 1.2V or 1.35V, but mismatched voltage can cause instability. Also, mixing single-rank and dual-rank DIMMs sometimes works, sometimes doesn’t. If your motherboard is picky, you might get crashes or failure to boot.

Best practice? Buy a matched pair. But if you already have a stick and need to add one, check the exact model of your existing RAM and buy the same one used or new from the same manufacturer. Failing that, match speed, timings, and voltage perfectly—and be ready to return it if it doesn’t play nice.