If your power supply is an LDO, you should find its noise vs. frequency plot in the datasheet. Most of the noise in an LDO comes from the bandgap, and it's largely pink noise. I don't know about the features of that software, but it's always possible to create a white noise source, and feed it into a filter to shape the noise vs. frequency, then create a voltage-controlled voltage source which takes this filtered noise as its input and outputs your "power supply" voltage.