Can't say I've ever seen it used. I've just looked at a 200W PSU and the -5V rail is speced at 0.1A so you couldn't run much from it anyway. Also I've never bothered adding the -5V line to my VIC 20 ISA backplane, I've yet to find a card that uses it. The one card that does have +/-5V analogue supplies uses 78L05 and 79L05 regulators from the +/-12V rails. Lee.