Something like this happened to me a while ago with a basic 30v/8A switched mode DC power supply. I think it was a Mastech brand, but I could be wrong. I was using it to power an innocent little project at 6 volts with only a few milliamps, when suddenly at random, the power supply decided to dump a steady 56 volts through the little thing and kill it!
Further testing relieved that the power supply was also in a consent current mode of around 8 amps. None of the output adjustment knobs had any effect on the output voltage or current.
It was replaced soon after by a more preferred power supply, but I decided kept the broken one, it seemed quite reliable for supplying the 55-56 volts that it was stuck at.
However, after weeks of abuse on the old one, while I was using it under a fairly heavy load for some extend period of time (the device lacks a cooling fan and will get hot), I heard a few clicks of the relays, and wouldn't you know it, it went back to its normal, advertised operation. I had my full voltage and current limiting controls back too!
I don't use this zombie-like power supply for any serous projects anymore for obvious reasons. It also recently decided to get stuck again in consent current mode at 8 amps. I still have full control over its output voltage though.
I only mention this because Dave seems to have fallen in a similar predicament where his power supply seems to send out its full current capacity at a higher then rated voltage (42.3v at first).