Optiplex 3040m hdd option

M(micro) takes 2.5 sata hdd/ssd.  in terms of power consumption, 3.5 hdd consumes typically 5-8w on average...up to 10w for mechanical drives.

A 2.5" mechanical drive will consume a bit less, because the discs inside are smaller and lighter, so the motor doesn't need as much oomph, torque, to keep the discs spinning. So a mechanical 2.5" drive will typically consume less than ~ 4-5 watts.

Drives Specification
Internally accessible 2.5-inch SATA drive.