Hi guys. Its me with the weird R9 280X doing 205 Sol/s
WALL:
Idle: 155 - 160 W
Mining: 290 - 310 W
135 - 150 W
(I'm only using my R9 280X)
They do use some power when idling too, you need to add that to calculations.
If you have one powered riser and a spare psu it is very easy to check. Wall - meter - psu - (riser + pcie power connectors), so only one psu that feeds only that one gpu connected to meter.
That leaves only speculations for psu efficiency.
I dont have any risers. I only use my main computer.
But yea. What would be a precise way to measure it.