These are usually noise supressors or mains suppression capacitors. They aree genrally rated to 440V and have capacitances around 0.1 to 2.2 uF.
For a schematic, use a geneal stepdown transformer and a linear regulator. If you are very careful you can just rectify the mains directly to get dc and then use a large (1M ohm resistor to drop the voltage) This will only work for very low currents.
Best off using a switch mode for high currents. Infineon have some good appnotes and parts you could use, that take mains voltages directly into them.