It remains true, as I said, that they have the same connections.
And in fact, laptop drivers require no more power than 3.5" drives.
I just looked at two drives that happen to be convenient to hand.
3.5": 5V @ 0.72A and 12V @0.52A
2.5": 5V @ 0.55A
Do note, however, that a USB port is required to provide only 0.5A at
5V, and the adapter itself will obviously use some power (thus the Y
cable or external power connection).
From my two drives above, you are saying that 0.72A < 0.55A.
I should look at another drive. Hang on a second.
OK, this is a slim-line 3.5" drive; it says 5V at 0.75A and 12V at
0.75A.
USB docks with external power supplies or USB adapters with external
power supplies should both work fine with both drive sizes; if they
don't, there is a problem somewhere. But who knows where?
USB adapters or portable drives without external power are another
issue...