So i wanted to do a test to validate the power consumption of PSI risers and determine what is safe for powering them based on their consumption.  I've heard many claims that you cannot use SATA cables, Molex, etc. due to the high power consumption of these risers.  Some posts I found stated as high as 65 W of power which is around 5.5 amps at 12V supply.  This power draw seemed unusually high too me.  Below is the parts list applicable to the test.

- Gigabyte Z270p-D3 Motherboard
- Intel G4400
- 6 x GTX 1070
- Zijiez PCI risers (excellent quality, highly recommended)
- 2 x Seasonic Focus Platinum 750W
- Newforshop electricity power monitor
- Running nvOC v0019

The test was simple, I determined the power draw of my normal rig.  I have a separate power supply which provides power to 3 GPUs including the PCI risers.  I determined the steady state power usage of my rig with all cards running and removed one GPU and recorded the difference.  I also ran the GPU at a different power limit settings to see if that had any effect on riser consumption.  Below are the results.

Rig running 6 x GTX 1070s with 115W power limit = ~ 800 Watts @ 0.99 - 1 P.F.
Rig running 5 x GTX 1070s with 115W power limit = 670 Watts* @ 0.99 - 1 P.F.
* Additional PCI riser still powered

Rig running 6 x GTX 1070s with 115W power limit = ~ 800 Watts @ 0.99 - 1.0 P.F.
Rig running 6 x GTX 1070s with 125W power limit = 860 Watts @ 0.99 - 1.0 P.F.

It should be noted that I noticed no difference in power consumption with the additional PCI riser card being powered or non-powered with no GPU inserted.

Based on the above, the difference in wattage between my 5 and 6 card rig was 130 watts while using a 115 watt GPU power limit.  I verified the GPU power consumption on my power monitor and in the driver settings.  This equates to a PSI riser consumption of around 15 watts.  Since I was running these on the 12V rail this is a little over 1 amp.  I noticed when I increased the card power that riser consumption did not change.  Perhaps i can re-run the test at higher power limits to see the effects.  

Even though the test shows that the power consumption is fairly low, you need to confirm your power supply can handle the load demand based on what connector you are using.  In my opinion it is best to power risers from the 12 V rail with a PCI power cable or a molex cable (both run off the 12 v rail).  SATA is not really meant to power risers and i'm no even sure why they design risers with this option.  Since they use 3.3 V rail this increases the current to about 4-5 amps (15 watts / 3.3 V =  4.45 Amps) per SATA power cable.  Based on the specifications below, if you are powering 5 risers from the 3.3 V rail you will be exceeding the rail power limits (4.45 x 5 = 22.7 Amps) which can damage the power supply or catch it on fire.  So in conclusion, power your risers with INDIVIDUAL (not daisy-chained) PCI power cables or molex cables and you should be okay.  PCI and molex cables both run off the 12V rail and this rail can handle the highest power demand.  

Seasonic Platinum Focus 750 Specifications
DC Output    Rail        +3.3 V       +5 V    +12 V    -12 V    +5 VSB
Maximum Power           20 A         20 A     62 A     0.3 A    3 A
                                      100 W          744 W    3.6 W    15 W
Total continuous power    750 W