random turn offs and restarts, low voltage?

Hi,
My desktop computer turns off randomly and restarts, and I'm not sure what's going on. I monitor the CPU temperatures regularly and I don't think that it's due to overheating. Tested the memory, no problems. OCCT test completes with no problems. I'm thinking maybe it's due to low voltage or volatility in power. I recently moved to Oregon to a newly built apartment. I didn't have this problem when I first moved in. But then I started using other appliances and devices, and I put an air purifier in front of my PC case, where the intake fan is, to prevent the dust going into the case. The air purifier has 3 levels and is connected to an outlet on a different wall. When I set the level to 3 (highest), the random turn off and restarts happen a lot. When I set the level to 2, my PC turns off and restarts only once in a while, but again, it's all random and it sometimes happens in the middle of an important stuff. So I'm thinking of buying a UPS as a solution. But is there anything else that I can try/do before buying a UPS?