iNFECTEM

Or, you can find a PSU, name it here, and me or someone else can tell you if it's good or not.
 
Simple

any high quality PSU with 750W or more wattage is enough,
 
you wanna look out for models with right models (Corsair RM, RMx, RMe)
 
Corsair:
Corsair RM750e (2023) 750 W 80+ Gold Certified Fully Modular ATX Power Supply
 
MSI:
MSI MAG A750GL PCIE5 750 W 80+ Gold Certified Fully Modular ATX Power Supply
 
Be Quiet!:
be quiet! Pure Power 12 M 750 W 80+ Gold Certified Fully Modular ATX Power Supply
 
Cooler Master:
Cooler Master MWE Gold 850 - V2 850 W 80+ Gold Certified Fully Modular ATX Power Supply
 
EVGA:
EVGA SuperNOVA 750 GT 750 W 80+ Gold Certified Fully Modular ATX Power Supply
 
Thermaltake: (Pure Power, Tough Power)
Thermaltake Toughpower GF1 PE 850 W 80+ Gold Certified Fully Modular ATX Power Supply

they re-assembled the whole PC

That's some pretty weird behavior.
Since the only thing you changed is the graphics card, that's the most likely issue.
It might not be faulty. You should reset those connections for PCIe and power. And might as well DDU while you're at it.

sounds like PSU related issue, not handling the transient spikes of 3070 well perhaps,
 
you might reduce the graphics detail, but the GPU will just crank more fps,
 
try turning on Vsync/forcing 60fps or lowering power limit of the GPU if you have an app for that and see if that helps (because if it helps, it might be PSU)

So what i do is get a gpu stress testing program. So first start bumping up all the parameters by 10: the memory clock speed, core clock speed, and core voltage. after you have done that run the stress test for about 2-5 min if you see everything is stable and you see no artifacts then repeat the process until you hit the max. for OC software i would use MSI After Burner (scroll to the bottom for download) and for the stress test i would use MSI Kombustor

You can also try using IOBit Driver Booster (free).
And SSDFresh to optimize the SSD.

Get InSpectre. Turn off the Spectre and Meltdown mitigations. Try after a reboot. Let me know.

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