Can i use sata to 6 pin adapter to power gpu ?
is it safe
I would suggest you not to go for a 1:1 Sata to 6 Pin. Which could give you a max power of 18 Amps or 216 W at 12 Volts max. Remember, these have precharge wires so it is generally not recommended for GPU's. Its a cheap alternative to getting a new external SMPS (which is pretty cheap these days). So it is best if you resort to using these only for your 'cheap' cards. You can easily damage the video card memory with these.
If you have a larger power requirement for your card, you could resort to using these :
https://sgcdn.startech.com/005329/media/products/main/SATPCIEXADAP.Main.jpgThese should be safer than the standard 1:1 adapters.