I have a question about the HP 1200W Power Supply and the x5 breakout when using whit a normal power supply. When I start the pc, the HP supply starting automatic? I don't need a start button for the HP supply?
HP 1200W and Corsair RM650x is enough for 6 * RX 580?
Or only on PSU Seasonic Prime Gold 1200W?
That button on the breakout board is most definitely the power switch. As far as I can see the circuit does not have any components to automatically switch on the PSU which means you have to somehow manually do it.
I just short out the signal ports on server PSUs to turn them on but you need to know or find by trial the channels you need to short out (although using a resistor is possibly a better idea). Sometimes there are several of them, i.e one for the turn-on signal and one for the there-is-no-fault signal.
And, HP 1200W PSU alone should be enough to power 6 GPUs. You can run it at 100% load 24h no problem. It's a real 1200 Watt workhorse. IF you're on 220V utility, that is.