I have same problem
And zero chance for fix it
I bouth a new one PSU..
And waste about 400 euro for all.
I have only one reccomend. NEVER TO BUY AMD PRODUCTION.
" ( i don't install any driver i'm don't know if this correct ) " Uninstall the video driver, run DDU driver cleaner than install the latest driver for your card.
Maybe the 265 driver is having issues with the 480.