I got my pico PSU from mini-box and the largest they have is 160w. Not to sure about the 180 or 250w or who even makes them. Also where would you get a power brick for those? After doing some searching I've only come across 200w power bricks.
I used an ebay 180w one to run an E-450 rig with a GT 430. But the brick that came with it is only rated to 120w so I can't really test its upper limit. I have measuring it working up to 100W on an Ivy Mini ITX build I used to test it.