I have only bad experience from external drive cabinets powered via the USB port.
A USB port can deliver max 500mA of current and that is usually enough to run a 2.5" harddisk.

Harddisk do consume more power when starting up and are close to 500mA for a short while before the mass starts rotating and they can after a few month of usage
require higher startup current.
Higher internal friction in pivots or bearings due to heat is one of the reasons.

I always use a separate power adapter with at least 1000mA (= 1A) rating and I am suprised to see that Seagate is selling this USB powered shite.