I said "The USB spec doesn't provide enough power for many typical 2.5" hard drives".
- Some drives are spec'd for the 2.5 watts power from USB.
- Some USB ports don't enforce current limiting to the 2.5 watts in the spec.
This is the "might work" grey area.
I have some external 2.5" drives that work with all my systems. I have some that work with some systems, but need the second "power" USB connection for others. I have some that work with some with the second power connector - but won't work with others even with two power sources (but they work with an external 5v power source).
I don't like "might work".