Exactly. It’s caught someone out before - there’s a post which I answered, I can’t remember when, it feels like a few months ago. The cable is already using (I think) 2 pairs for the power (Pins 4+5, 7+8). You’d need to check the instantaneous maximum current as the Pi starts up and look up the voltage drop for the particular brand of cable The Shop has supplied with yours, to get an accurate assessment.
[Edit] This was the earlier topic: EmonPi2 only displaying "starting"