(230v)AC-DC(12v) wall adapter flashes when connected to dc to dc buck converter
Since the input capacitor has a low ESR the surge current may be up to 12V/ESR.

If the supply starts up with the Buck connected then a slow start might work with a suitable ICL, Inrush Current Limiter.

Ic = C dV/dt  Choose 1A or get a variety of values with a 12~22  Ohm minimum R @ 25&deg;C

TI's standard design shows 27uF 40 mOhm for Cin.  Thus if the 12V output is cycling On and OFF with the Buck regulator connected, 12V/40mOhm = 300A ( in theory ) but in practice limited by supply.



Recommendation:


Use a 1A ICL for a 1A source.
use a DC source with a soft-start and larger surge capacity such as a 19V 65W Laptop charger.