We tested the peak power consumption of a NAS at the wall during a run of CrystalDiskMark 5.0.2 as this version of the benchmark runs the read and write benchmark suites separately so its easier to monitor what power the device is using during each function.
Synology quote power consumption figures for the DS418j as 21.22W access and 8.97W in hibernation fully loaded with 1TB WD Reds. The 6TB WD Reds we used to test with have a 5.3W read/write rating compared to the 3.3W rating of the 1TB version so our figures were a little higher. Both drives have the same 0.4W standby rating.