You may have exceeded the USB(I assume) port ability to provide power. These are meant to be simple ports. If power is being supplied, then that's your problem. Plus, if you have both at the same system port area(hub) then again its an issue. I suggest you place these ext. HDs on a self-powered USB hub if none is supplied by the ext. setup itself. Also, if not already use rear USB ports if possible when no ext. powered hub is present.
As for cheap parts, IMHO that's the result of end-user buying ability. Its not entirely the makers fault when costs get out of hand. However, in electronics having lower costs does immediately become applied and that's not necessary the cheap route. Its just cheaper to build and yes those same components do alot for very little as electronics improve and shrink. As for the power connections, these too are very simple and needn't be as robust as what's supplied is sufficient. But, they aren't forgiving to repeated reseating though, handle w/care.
I just bought 2 Seagate external drives. One is 1 Terabyte, the other is a 1.5 Terabyte FreeAgent. The FreeAgent would NOT STOP CLICKING ON AND OFF, or SWITCHING On and Off). The 1T drive did it some too. I wasted HOURSSS formatting, re-copying, doing "Extended Drive Tests".
Turns out ... they have CHEAPENED the drives to such an EXTREME ... that the power connectors don't connect well ... and so the power is affected just enought to cause this. They even took the "SMART" feature off the drives....... I switched power cords between the units ... and now they work fine. NOTICE how light and flimsy and cheap the hard drive is now ... even though the capacity is doubled or tripled !
I'm so pissed off. Both drives are now compromised because the cheap circuit board and switche... Clicked On and Off, Switched On and Off, .... hundreds of times .... so God only knows how long before they burn out.