Can someone look at this cable and tell me what it is (front panel cables)

Solution
That's for the Phanteks case's LED lighting power. Connect that plug in one of your PSU's SATA power cable (the ones you also use for the HDD/SSD power) that looks like this:
cp-8920113_sata_conn.png


It *might* not be required to be plugged to boot (but it may disable some front panel functions - esp. the LEDs). But, most likely, if you don't plug it in, you'll just have the LED case lighting disabled. Still, to be sure, just plug it in.
That's for the Phanteks case's LED lighting power. Connect that plug in one of your PSU's SATA power cable (the ones you also use for the HDD/SSD power) that looks like this:
cp-8920113_sata_conn.png


It *might* not be required to be plugged to boot (but it may disable some front panel functions - esp. the LEDs). But, most likely, if you don't plug it in, you'll just have the LED case lighting disabled. Still, to be sure, just plug it in.
 
Solution