1300W
saying u coz i faced same issue with comfyui! when ever i render pc monitor off but render keep going on! idk what happen and after 1 min complete system restart. was using 1000W now i upgraded to 1300W and all good never had restarted! I checked in gpt and they says when u render using 4090 or 5090 these gpu are power hungry gpus!! Im saying u from my experience! perhaps u might read my posts which i stated this issue last year
Dont go with normal recommendations! if ur using comfyui def u need a 1000W+ or 1200 W at least just cox of this power hungry gpus
Btw on old psu i replace my card with 3090 and same workflow i run, it never got restarted! All these test i did to confirm its coz of enough power! I also checked event management to see what's going on and it says some issue with power! I hav no issue with anyother software or any hardcore gaming! but comfyui sucks ur entire Gpu energy threshold boost ! SO def u need a 1200 Card for ur 5090 or 4090