Correct me if I'm wrong, but the reason all external bricks are 16-19v and only go up to 330W is because they are all meant for laptops. Clearly 12v is better, and you can go up to 500W within a fully sealed external brick. I used to think it was an engineering limitation (i.e. you need a fan over 330W), but that's clearly not the case with 94%+ efficiency and larger bricks (make it huge, I don't care). They can keep units at 19v, because laptops will always be a much bigger market, but they should at least step up the wattage of bricks to 400W or 500W. There are laptops now with dual power bricks, which is ridiculous. HDPlex could make good money from selling their own external bricks in addition to their internal AC-DC, and also step up to 400W. If one guy in China can do it, why can't big companies?
Really, 400W is what you need to do a 91W CPU + 250W card and 500W is what you need for a 140W CPU + 250W card (with moderate overclocks). There's no reason why power should be a bottleneck in tiny powerhouse systems.