Figure 3 and 4 show the noise performance difference between two types: switching and linear regulator. In small signal measurement, noise performance an important factor.
The switching power supply has a lot of large noise at switching frequency and its harmonics (Figure 3). And it has also large humming noise (50 or 60 Hz and its harmonics).
Linear regulator type power supply noise is lower than switching power supply one. However, humming noise may exist due to superimposing in magnetic noise from the power transformer and common-mode coupled from commercial power supply (Figure 4).
Moreover, the disturbance noise may mix in output voltage at both type (Figures 3 and 4). This noise is due to poor shielding of the instrument or humming noise superimposed from the commercial power input.
Related keywords : Low Noise DC Voltage Source