Switching power supplies can generate some nasty RFI spurs.  

Now, some designers are turning toward "dithering" the power

supply switching frequency courtesy of a built-in random number

generator.  With this approach, instead of having a lot of RFI on

one frequency, the RFI will be thinned out and spread across a

wide spectrum like cheese on a cracker.  See:

 http://powerelectronics.com/mag/603PET07.pdf
 

Apparently this is cheaper than building in filter components,

hence improving the profit margin for the manufacturers