1, switching power supply can't be used as signal source, otherwise the signal output by precision instruments will produce errors.
2. The switching power supply can't provide a regulated power supply for precision instruments, because the switching power supply is a pulsating power supply, and the voltage will change with the pulse, so it can't maintain the stability of the voltage, so it is not suitable for being used as a regulated power supply.
3, switching power supply will release electromagnetic waves, will interfere with the surrounding electronic equipment and signals, so it is not suitable for precision instruments.