I can't answer your question about PSU polarity, but I do have some experience with the Mac Portable hard drive. I had to 'make' a replacement drive for one, almost 20 years ago now.. so forgive me if there are errors in this! You're correct about the drive connector, it's one of those maddening proprietary things that Apple was and still is prone to doing. If I recall, the drive itself uses the standard SCSI interface, but the stock drive has a permanently attached cable with its own pinout. And I think the drive cable carries both data and power. If you can find the +correct+ 20 or 40MB (?) Conner hard disk, you can make a cable that allows you to use one as a replacement for the stock drive, which is very prone to failure. Apparently, the stock drive is a low-power version of the otherwise identical Conner drives available at that time. The stock drive has a red label, and if I recall, the similar but not-low-power drive has a green label. So the common green-label drive works fine, but it will consume more battery than the special low-power version. Point is, if it still exists, find the web page that shows how to make & wire the adapter cable - and that should give you enough info to create a data & power cable that will allow you to read the stock disk. There was also some talk, at the time, that it was possible to transfer the complete circuit board, with cable, to one of the green label drives.. and have it work. Of course, this would only work if the drive had a physical failure, rather than a failure with the board electronics. In my case, I had to wire up a special cable.. it took a couple hrs, but worked fine. On Sat, Nov 26, 2016 at 12:26 AM, Chris Pye <pye at mactec.com.au> wrote: