Bad power supply. not at all 95% efficiency. 511w with my previous PSU move to 547w with exactly the same configuration. Furthermore, cables are too short to power GPU and riser on the same cable. So you have to use extension if you want to connect 8GPU. Finally, I paid 38€ duties because seller did not declare low value ( I requested, never answered). His only proposal was to send it back and lost money!
very good