I use this:  CHIEFTEC A80 750W PSU.
The win10 was a clean install and I use the afterburner too.
At the moment there is two videocard PSU connectors are divided to four so one rail us divided to two way.
I have not tried the "i -3" but I will, thank you for the advice!

My config:
-zpool eu1-zcash.flypool.org:3333
-zwal
-zpsw z
-i 4,4,4,4
-r 1

And settings:
setx GPU_FORCE_64BIT_PTR 0
setx GPU_MAX_HEAP_SIZE 100
setx GPU_USE_SYNC_OBJECTS 1
setx GPU_MAX_ALLOC_PERCENT 100
setx GPU_SINGLE_ALLOC_PERCENT 100