Yeah, bummer on the powerbook.

The basic spec is that many 2.5" drivers draw 5W of power during spin-up. Since they're running off of 5VDC, that means 1Amp. USB2 ports deliver 0.5Amp.. thus..

Some 2.5" enclosures include a funky cable with TWO USB-A connectors, so that it can draw power from two ports instead of one, for a total of 1Amp.

Others include obscure wording and references to external AC adapters and PS/2 power sources and stuff.. but the one's I've seen have never really explained the basic problem/risk with powering them from USB.

Most of the time it works fine, though.

Cheers