Can any power supply be made a current source with this circuit?
There are a few problems with using a DC to DC converter as a 'power supply'.

The first one is stability, most DC to DC converters are only stable across a certain range of voltages.

The second one is dropout, most DC to DC converters drop out on the low end of the voltage range. The LT1076 is stable across this range, from the datasheet


  Buck Converter with Output Voltage Range of 2.5V to 50V


So conceivably you could use the current limiting function but after 2.5V it would drop out.

There is a schematic that I've seen from linear (that I can't find right now) If I remember right it uses the LT3042 (or simmilar LDO) to drop the remainder of the voltage down to get the full voltage output range.