Have a look at this:
My PSUs start up at the same time due to the spliced PS_ON# lead.
As the 2 PSUs are exactly the same, I do not care about different starting times.
All molex connectors of the raisers go to PSU1, which is connected to the mainboard, the extra 2 molex on the mainboard, CPU power, and 3 of the RX470.
PSU is stripped down to just the PCIE leads + PS_ON# and power the last 3 RX470. Ans sometimes there was like 2 or 3 seconds between switching on the 2nd PSU. And nothing burns. 
Before I hat the PS_ON# spliced, I just turned on the PSUs with the switch on the backside.
So for me this is working. If you are in doubt, go for 1 single PSU with 1000 watts. (1200 watt to hit the load sweetspot)