Keep in mind with some of those 2.5" SCSI Drives (later SCSI). Some of them used 12 Volts, especially the faster RPM models. Much like the WD Raptors and other SATA 2.5"/SAS 2.5" drives, they almost always required 12v, which the powerbooks did not provide

(I still get a kick of the people on forums complaining that when they did somehow manage to show-horn a 2.5" WD Raptor into their laptop, for "Some" reason their drive won't spin up...)