What is the power factor of a power supply?

The power factor or cos phi of a power supply is the ratio between the real power and the apparent power.

A purely resistive load (e.g. a heating coil) has a maximum power factor of 1. The power factor can be reduced either by a phase shift between the voltage and the current (for inductive or capacitive loads) or by a current with a non-sinusoidal (not sine-wave-shaped) curve (e.g. a power supply).

The apparent input power (VA) can be measured in the input wires with a voltmeter and ammeter. The apparent power is the product of the current and voltage.
To measure the real input power (W), a wattmeter with an adequate bandwidth is required.

The input current of a power supply can be calculated using the power factor and the efficiency, if the output power and input voltage are known.

The PULS datasheets include characteristic curves for the power factor based on the input voltage and load.