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.
Interestingly, power draw for the overclocked TUF Gaming X3 RX 5700 is lower than the reference model. It could be ASUS' custom PCB design is simply more efficient, but our system pulled 14W less with the ASUS card than with AMD's reference design.