Inductance of a practical relay
The coil inductance is generally not important. In the case of your SMPS the inductance will result in a more gradual increase in current when the relay is connected than a resistor of the same value as the coil's resistance would.

The reason to care about inductance is generally not about switch-on but about switch off when you need to have snubbers fitted to prevent inductive kickback affecting the supply.

Also, I would expect that the inductance will change when the armature closes as the magnetic circuit's reluctance will be reduced.



That got me interested. I had no idea what the inductance of a relay would be so I measured one using my EZM328 V1.10 component tester. (These are amazing little devices and are available for about €10.) 



Photo 1: Relay, Finder Type 40.51, 24 V coil. Note the open armature arm (1). Not visible is the core running through the coil and the steel fixed part of the armature running up to the hinge.



Photo 2. The test setup.

As can be seen in Photo 2 the results are R = 871 &Omega; and L = 3 H.

For the second test I held the armature closed by hand. What do you think the inductance reading would be with the armature closed? (Hover over the spoiler to see.)


  Answer: 8 H. This is a gain of 166%!