We've measured the power consumption during two scenarios: idle (where we determined an average based on 5 minutes of idling) and under load, where we measured the maximum power consumption during Cinebench 15.
Do note: from this generation onward we use a different (and extremely efficient) power supply, which means that the measured power consumption will differ slightly from previous measurements. We also configure the motherboards differently: everything is tested at default settings of the BIOS now.
The ASRock Fatal1ty Z270 Gaming-ITX/ac is extremely power efficient, during both scenarios. It's even more power efficient than the MSI Z270 SLI Plus when idling, the previous most power efficient board. It's also 10 watt more power efficient under load than the ASUS Z270-A Prime. These results are exceptionally good, especially if you consider that Mini-ITX boards are not nearly as power efficient as the stereotype says.