Well, it seems using 2x8 pin rather then 1x8pin+1x6pin made the difference, works now.
Not a fan of using 6 to 8 adaptors(never have).
Depending on the age/make/model of your psu, the 6 pin is probably using lighter gauge wiring.
Pulling excess power above it's rating may cook the wiring back to psu.
Why risk blowing an 800 dollar card(no warranty on psu failure).
It is a Corsair RM750x, 18 AWG, The wiring is not really the limiting factor in these connections, it is the plugs. the ampacity of a single 18ga stranded copper is 14A, the 6 pin has 3 of these so the wires are good for 42A or 500W @ 12v. Molex Mini fit Jr. plugs are rated to 9A per contact x3 contacts = 27A or 324 W @ 12V. This should be fine for a non overclocked card, but I would probably run separate 8-pins if I was overclocking. (I am an industrial engineer, I do this for a living)
All good then, you don't have a $20 firecracker psu..
Yeah, dumb thing is the 8 pin plug I have used to have another 8 pin plug on the end and I cut it off th help clean up the wiring since my rx480 only used one 8 pin...live and lern.