We measure system-wide power draw from the wall while running the 3DMark Time Spy stress test for 30 minutes.
Total system power for the RX 6800 is in-line with the RTX 2080 Super, with the system drawing about 360W at the wall.
We also use Nvidia PCAT to measure power draw of the graphics card only, with readings from both the PCIe slot and the PCIe power cables combined into a single figure. This provides us with significantly more accurate data to work with as it is measuring only the GPU power, and not total system power which is a fundamentally imprecise measurement.
Looking at GPU-only power gives us a clearer picture. Despite its 250W total board power rating, we saw the RX 6800 average 237W during our testing. This is 22W higher than the RX 5700 XT, and 18W higher than the RTX 3070.