How do these tiny power supplies work?

http://www.aliexpress.com/store/pro...t-DC-DC-PC-Power-Supply/211500_553436047.html
http://www.aliexpress.com/store/pro...t-Plug-In-Power-Supply/211500_1901387831.html

The website and products I linked are just an example, but I have a miniITX project in an extremely tight case and my question is do these little things work like a regular power supply?

I'm mainly looking for a product to power a (rated) 200 watt AMD APU build inside of an extremely tight case. (The case is less than an inch larger than the miniITX board) I want the power supply to be as small as possible and as internal as possible (No giant PSU sitting outside the case). I'm more than fine with using a "power brick" that laptops use but I cannot find any such products for desktop PCs.

They accept a connection from a power supply like this:


And turn it into something that can be used by typical PC hardware.