The growth of companies that make external USB hard drives has grown immensely in the past few years. At the same time the capacity of these external harddrives has grown as their overall size and price have plummeted.
No. "2.5 hard drives in enclosures are essentially identical to normal external hard drives (most "external hard drives" are just laptop hard drives with a case and USB logic) - they need no power adapters. You're probably thinking of bigger "3.5 enclosures for desktop hard drives - those things do need more power than USB can supply.
Thank you for the inside information, but remember there are two type of external hd, the higher capacity drives like over1tb usually come with power adapter. the few laptop 2.5" SATA hd I changed also need to connect to power source.
Thanks