Apropos, I just installed a softstart addition to two isolation transformers (545 VA toroid). I finally got bored to change the fuses (sometimes several times) on each restart
My approach was to use just 5x10 ohms resistors in series of the primary, and relay which shorts out those resistors after 500 ms or so. Although NTC is simple, I don't personally like idea of a hot component and it doesn't work on brief disconnect. It took a little iteration to get the switching action quick on disconnect, so that softstart works properly even if power is only briefly disconnected. Seems to work very well. Theoretical maximum inrush current is therefore 230 V/50 ohms = 4.6A, which seems to be low enough for the fuse to handle. Relay and time delay circuit (just some discrete components) is powered through a "cap dropper" supply, using a 330 nF X2-grade capacitor.
Now I can use 2.5A slow-blow fuses (nominal for the transformer), before even 3.15A slow-blow fuses usually blew on power-up.
Note that fuse shown on the softstart PCB is not the main fuse, that one is just protecting the softstart resistors in case the output is shorted.
Regards,
Janne