Paruht Power Sharing Cable 0.2 m PC ATX Power Supply Convert 24-Pin to 14-Pin Cable Main Board Adapter Cable 20cm  (Compatible with 14-Pin Male for Motherboard, 24-Pin Female for ATX Power Supply, Black, Yellow, Red, One Cable)

This is safe as the motherboard gets power from only one PSU. The second PSU provides power to the other components. Both PSUs start by pressing the on / off button of your Type: Main Board Adapter Cable Instruction: 24 Pin Female for ATX Power Supply,14 Pin Male for motherboard Length: 30cm Material: 18AWG Standard Wire Type: Main Board Adapter Cable 14 pin male connected to the motherboard, 24 pin female connected to the ATX power supply. Instruction: 24 Pin Female for ATX Power Supply,14 Pin Male for motherboard PC power supply upgrade manually convert 24 pin to 14 pin connector.