For testing power consumption, we took our test system and plugged it into a Kill-A-Watt power meter. For idle numbers, we allowed the system to idle on the desktop for 15 minutes and took the reading. For load numbers we ran Battlefield 1 at 1920 x 1080 and recorded the peak power number while gaming a particular level that we test on each card. Our idle numbers are high, but keep in mind that we are using a workstation motherboard that has two 10GbE ports and other high-power draw controllers on it.
Power Consumption Results: With the Sapphire NITRO+ Radeon RX 580 LE installed in the system we topped out at 412 Watts when running BF1 at 1080P resolutions and used 147W at idle. Not bad power numbers, but the GeForce GTX 1060 FTW card by EVGA topped out at just 315 Watts, so this particular NVIDIA card at times uses nearly 100W less power!