what make/model 1kw PSU?
How are your CPU/GPU temps?
Are you overclocking anything?
Are you running any cable extenders INSIDE your case like a PCIe riser cable .. modded power cables ..etc ..?
My wife's 5900x would reboot when the door where her computer sits would be closed when running CS2 .. I bought a better CPU cooler and now her CPU doesn't come close to the thermal limit it was dancing around before