I have just completed a 21 page document on this switch-mode supply from the early 1980's. IBM did not publish data on it.
http://worldphaco.com/uploads/The_IB...WER_SUPPLY.pdf
It contains a range of different circuit innovations including surge limiters that use a PUT, current detectors with a current transformer, modulated base drive for the switching transistors with current feedback to improve efficiency.
One idea allows the use of a transformer with a 115V primary to be run from a 230V supply (for the 115/230V universal power input select circuit). It is a good method to synthesize what amounts to a low Z reference point that splits the incoming 230V mains in two. This idea would be suitable for running many small transformers in small 115V appliances from 230V without the need of a stepdown transformer and better than a series resistor or reactance as the method relatively independent of the load. It requires a bridge rectifier and two high value 200v electrolytic caps.