Funny you should ask...
I just built a PCE Briefcase supply yesterday, I used a 9V 1.7A Switching adapter bought at an electronics store for about $16, the correct negative tip/adapter for it was another $1.50.
Don't sacrifice your genny power brick unless you don't have the $1.50. The IFU-30 or Interface unit is negative tip, unlike the Duo which is positive tip so make sure you have the right power supply, or you can do some damage. I'm not sure of teh genny adapter's polarity, I've recommended against using these in the past. If you get a multi-head generic adapter (they run around $25); you can get one of those little cables that allows you to switch the polarity of the wire.
I have a multi-tip that use for testing dead units, and its ok, but I prefer to build a supply for each unit so it doesn't get confusing.