MH>I work with large Cisco networking equipment at work.  The large chassis can   
   MH>can take different power supplies.  Some will run at 110v or 220v.  You can   
   MH>a 4000 watt power supply that will run at 2000 watts if connected 110v or th   
   MH>full 4000 watt if connected 220v.  I assume that is due to the single vs. du   
   MH>phase connection?   
      
   Typicaly in 110/220 equipment the power transformer has two primary   
   couls. They are connected in parallel for 110 operation and series for   
   220 operation. Normally that would give the power supply the same Watt   
   rating.   
   The dual rating power supply apears to be designed to use a single   
   primary transformer and the output rating would double becasue of the   
   doubiling of he primary fees with 220 input vs 110 input.   
   Of coruse extra electronics woudl be involved to the correction the   
   higher voltage to maintail the same power supply output to the   
   equipment.   
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