Try as much as possible to avoid any s-ata adapter or even molex adapter connection for powering up risers! Sooner or later, it will melted.
S-ata powers are good until around 25watts consumption (for biggest hard disk), but PCI-e adapter can consume more than 80 watts when delivering 75 watts to graphic card.
The best riser power supply connection, is directly PCI-E 6 pin connector plugged into it.