but my cards sapphire nitro 570 each one take 6 pin and 8 pin = 190 watt for each card . is the molex cand to power third card which has 8 pin only with causing instability keep in mind i have one molex wire with 5 or 6 heads of molex
There are 5 peripheral connectors on the back of your PSU for molex/sata cables — do you have 5 cables for all those connectors or do you have less than 5? Some psu mfgs include full sets of cables in the box with PSUs, and some only put like 3-4 cables even though there are 5 connectors. When running 3 cards in total, and all 3 are on powered risers, you can use 3 out of those 5 cables to power the risers for all 3 cards, and the remaining two for the 2 adapters (molex=>pci-e or sata=>pci-e) you'll need to power the 3rd card. You can use any of those 5 cables to connect your hard drive as well since it won't consume more than 10 watts (or even less, if it's an SSD) so it can share one line with any of those.