Buck converter mains voltage
One problem with a large voltage ratio buck converter is that the duty-cycle becomes very small - the ratio of the voltages - and if you maintain a reasonable frequency of operation the ON time gets very short.

Also the way you have it here with an N-channel FET the PWM signal is required to be over 130V in amplitude - this will be difficult to create, especially as it is above the maximum Vgs of the switching FET.

A buck converter is non-isolating so the output is galvanically connected to the AC input - potentially a safety issue.

Also - why do you specify 127V as the input? If it is really AC line power at 120V when you rectify it you will get ~165V.

The normal solution to all these problems for low to medium power is a flyback converter using a transformer.  These can be very simple, although it is usually simpler to purchase a ready made unit.



From SMPS schematic

Design Guide for Flyback Converter