lightfoot, is this a common problem with the HP common slot PSU's? I had the same problem recently using Deepinthemines breakout boards with 750w PSU's
The root of the problem is either wires that are too small to the plug, or a power supply that sags under load. The sagging thing is interesting, if the voltage drops to 10v, the current has to go up to maintain the load. Since P=IE (mmmm, pie!) lower E=higher I. Which causes more heat, which increases the resistance of the pin which leads to more voltage dropped and the usual burning.
I use the Emerson supplies myself with 16 gauge wire plugs. No problem there. In terms of getting the plugs off I find that using some good old rosin/lead solder on the pins first (to allow with the ROHS) REALLY drops the melting point a nice bit and makes it easier. You can also get some chipquick. :-)
C