Some of the external USB drives are picky about power on the USB ports they are plugged into and won't work properly or moan and groan and go ti-tik-tik.
One that I have doesn't like the ports on the front of PCs.
Generally I prefer Western Digital to Seagate, but that's just a prejudice.
Try before you buy if possible.
Edited to add: The 1st generation and luggable portable drives all have a dongle separate PSU, and as Heathrow Director says below, obviously didn't have power probs. but the PSU is just one more damned dongle to cart around...
The pocket drives now can run off just USB power but, as I said, some are fussy.