We measure system-wide power draw from the wall while the card is sat idling at the Windows 10 desktop for 30 minutes. A reading under load comes from running the 3DMark Fire Strike Ultra stress test for 30 minutes.
Power draw is another interesting area to look at, and right away we can see AMD has improved its overall efficiency significantly – total system power draw is down by 70-odd watts compared to the RX 580, despite 5500 XT also proving the faster card.
Then again, this is still almost 50W higher than our figures for 1650 SUPER, so Nvidia clearly still has the edge here with its Turing architecture.