Converting universal AC to 3.3v DC @ 0.1A

A device like the Power Integrations LinkSwitch-TN allows you to implement a simple buck converter that converts rectified mains voltage to a reasonably-well-regulated non-isolated low voltage with reasonably good efficiency.

If you need low ripple after the fact, you can put a linear regulator on the stepped-down output of the buck and minimize your resistive losses.

I've used these as primary-referenced control supplies and have had good success with them.