Hi.

What you Experiencing is what I Call EMP, Even though it is
not a real EMP, Its kid of the same result. when you
withraw a very high power, in the begining of the
operation, the 300W PS is drawing alot more than 300W for
initial, then it reaches to its optimal operation.
anyway, try to put your circuit inside any METAL Case, and
connect it to the ground. Also use some capacitors:
0.1uf,1uf,10uf,100uf - All of them, not one, and connect them as close to the MCU As possible.
It had worked for me, With NEON Transformer.
Goodluck.
OK