Inrush is a real bitch. I make it a rule to include simple inrush current control circuits whenever I do DC input that sinks more power than, say, a USB cable.
Lotsa surprise inductances out there. I've felt your pain re: inductance + input cap creating a resonant tank, too. That's a nasty surprise when you manage to create that resonance with your wiring.
The worst is when the other guys think you're crazy because they're not suffering the same problems because either the smps they have had a soft start or they overspeced the living crap out of their input stage. I gave up and just spend the 5$ for the IC that provides slew rate control, single IC with a single fet? Oh hell yeah.
Lotsa surprise inductances out there. I've felt your pain re: inductance + input cap creating a resonant tank, too. That's a nasty surprise when you manage to create that resonance with your wiring.