Probably works, but don't count on it.

You can try, and it often boots. But mixing brands, speeds, or timings is a gamble. Even if it works at first, you might get random crashes, instability under load, or the system will downclock both sticks to the slowest common denominator (usually JEDEC defaults, not XMP).

Dual-channel wants matched pairs. Same brand, same model, same speed, same timings. Mixing 3200MHz with 3000MHz? The faster stick slows down. Mixing different CL ratings? The looser timings win. Mixing single-rank and dual-rank? Possible but more unstable.

The real headache: you might not notice the instability for weeks. Then your game crashes mid-raid or your PC refuses to wake from sleep. Then you spend hours testing sticks.

Your odds get better if both sticks have the same primary timings and voltage, but even then, subtle differences in memory chips (Samsung vs. Micron vs. Hynix) can cause grief.

Save yourself the headache and buy a matching kit. Selling your old stick and buying a 2x16GB kit costs less than the frustration of chasing ghost crashes.