@rogeriosmorais:
Sata Power only got two 12V lines, each for 1.5A = 36W total
4-Pin Molex are 5A on 12V = 60W
PCIe x16 is specified for 75W and you can find pictures of burnt sata and molex plugs which were used for risers
Sata connectors have 3 12V pins for a total of 54 W. The SATA cable and connector are rated to handle 4.5A over each of the 3.3V, 5V and 12V rails for a total of 91.35 W.
http://www.playtool.com/pages/psuconnectors/connectors.html#sataPowered risers draw less than 50 W and are perfectly safe to use with a SATA connector. Burnt connectors are from overloading the cable by using more than two connectors per cable strand MAX or using a Sata connector to power a high draw card.
You can use an 8-pin splitter cable into dual 6 pins to power the card and riser on the same cable.
https://www.amazon.com/Phobya-PCI-E-Splitter-Cable-Sleeving/dp/B00A5TA7NG