Hrm, maybe over USB it's different because of the performance limitations, but my understanding was that SATA was lower power draw.

Though maybe I'm wrong and/or potentially this differs on a per-drive/per-controller basis.

It very much depends on the particular drive, with both controller and NAND choice affecting power draw and efficiency.

On a performance per Watt basis, most M.2 NVMe SSDs are much more efficient than M.2 SATA SSDs. The most efficient M.2 NVMe SSDs are also at least competitive with M.2 SATA SSDs in terms of absolute power consumption, despite outperforming the SATA SSDs by at least a factor of 2-3x. Power consumption from a M.2 NVMe SSD will also drop slightly when only one or two of its four PCIe lanes are used, which is the case when the drive is behind a USB to NVMe bridge.

For example, comparing a SK hynix NVMe drive against of dozens of other M.2 NVMe and 2.5" SATA drives: https://images.anandtech.com/doci/16012/rr-all.png Unfortunately, I don't think there are any M.2 SATA results in there, and those are often a little bit more efficient than their 2.5" counterparts (running off 3.3V rather than 5V, but stepping it down to at least one or two lower voltages on the drive in either case).