I talk crap about his rigs, cause its obvious he is trying to sell them here, and this thread is not for that, so I agree lightfoot.
Overclocking a 390 is really unnecessary on Ethereum, in fact you should undervolt them, I power my 6x390 rigS with EVGA 1300W and even Thunderbolt 1200W.
So there is absolutely no need for a 2PSU setup + 390s are not as effective as 380s price/hashrate/power
If you r interested, look at my older posts, you can see my rigs evolving for 5 years from rigs in fruit crates, to rows up on rows of rigs.
Im selling what the customer wants, that is more mh for an acceptable price. No im not trying to sell here, just showing some work im proud of.
Offcourse you can undervolt to best mh/w ratio but thats not affordable to sell.