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 it's easier to monitor what power the device is using during each function.
The Intel Celeron J3355 dual-core CPU in the TS-251B has a TDP of just 10W so with some careful choice of hard drives, the power demands of the NAS can be kept quite low. The WD 6TB Red drives (WD60EFRX) we used for testing have an average read/write rating of 5.3W, with a 3.4W idle rating and just 0.4W when in standby/sleep.