Soft Start Inrush Current Limiter- PCB design

[m_c]

SSRs typically switch at the zero crossing point, however that is the worst point to switch as it'll cause the biggest inrush, which is why they're a poor choice for switching transformers (plus the fact they generally fail short circuit isn't good from a safety perspective)

It only takes a couple cycles for the transformer to fully magnetise provided it receives enough power, but it usually takes longer than a few cycles for the power supply voltage to recover, which is why you want a slight delay.

Personally, provided the transformer isn't going to be switched off and on regularly, I just use a thermistor. Not technically perfect, but adequate and far less likely to go wrong if sized correctly.