Yes you need more power supply for sure.
Er no offence citricacid - but if you are using 400w per card you are doing something really wrong!!
What kind of measurements have you done with 1080ti coz they are way higher what I get with mine.
I get the following per 1080ti:
124w @ 473sols
148w @ 598sols
176w @ 642sols
198w @ 685sols
224w @ 721sols
249w @ 734sols
286w @ 769sols