DC/DC converter to go from 12VDC to say ~250V. How to avoid switching noise?

[777funk]

I've done this twice now and it seems difficult to avoid the very high frequency noise. It's much different than the usual 50/60 Hz problem we face with traditional transformers and FWBR diodes with caps, resistors, and chokes.

How can I use a DC/DC without this high frequency noise?

 

[ccaudle]

Buying a pre-made DC-DC converter, or designing and building your own?

 

[Khron]

How can I use a DC/DC without this high frequency noise?

Additional (LC / RC) filtering. Especially since, presumably, it won't be a particularly high-current supply..?

That, and proper ground connections.