Best way to get a low DC voltage from a high DC voltage for a power supply?
http://www.sparkfun.com/products/10214 

While this charger is rated for 100 - 240 VAC, the first thing that a switchmode supply does is rectify the input voltage, so 200 VDC will work fine to power it.

(You can of course buy this kind of supply in a variety of output voltages.)