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.