PSU Confused on DC-DC power supply wattage.

I'm looking at getting a 200W DC-DC power supply (here) for an HTPC.
What I am confused about is do I need an AC-DC external power adapter that has an output of 200W in order to get 200W out of the DC-DC?

 

if you want to run it from AC (mains power) then you will need a AC to DC converter of the same wattage in order for it to function.

 

You'll need a mains transformer of at least 200W to power it.

 

Thanks guys!

Edit: Do you know where I can find a 200W or higher AC-DC power adapter? The highest I can find is 150W.