Should I use a switching or linear power supply?

You should be able to use either a switching power supply or a linear power supply to power the HI 3000 or HI 4000 series units as long as it has a sufficient power rating. This applies to the HI 3000 series, HI 4000 series, and HI 6000 series units. See the technical manual for the specific model you are using to determine the power requirements.