What's the preferred way to measure system or CPU power usage, aside from "at the wall"?
HWinfo64?
Others include, but are not limited to: power consumption meter at the wall (between wall socket and PC power plug). <- Have that (namely MacLean Energy MCE06 230V/16A wattmeter). Bought it prior buying UPS, to know how beefy of an UPS i need.
Another option is UPS that has LCD display. So you can look exactly how much power is delivered via UPS to PC. Aka how much power your PC consumes. For added convenience, UPS that connects to PC via USB cable, so you can check the power consumption from software, either dedicated one or from HWinfo64. <- Have that too (CyberPower CP1300EPFCLCD).
Overall, there is no "preferred"...