Originally Posted by dhughesuk
so it's pulling 520W but can only give 80ish% of that due to efficiency?
It all depends on what your system is pulling from the PSU.
So let's say your system is pulling exactly 350W from your PSU under full load. If your PSU is 85% efficient, then that means it is pulling about 412W from the wall in order to deliver that 350W to your system. So if your PSU were 100% efficient, then it would pull 350W in order to deliver 350W. Those 62W are lost as heat, but that's not bad considering that 5+ years ago or more, 70% efficiency was a bit common. So if your PSU were only 70% efficient, then it would have to pull 500W from the wall outlet in order to deliver 350W. Fortunately, the capacity rating of PSUs is regarding how much it can deliver to a computer system and not how much it can pull from the wall.
So yeah, it all depends on what your system is pulling from your PSU.