Powering PC from external PSU

[thewipyk]

Hello guys!
I recently found an old rack case in which I'd like to build a PC out of pure fun and testing my modding skills. I searched for multiple power supples that would fit in, but unfortunately they are either too big or have too low wattage.
The case's inner dimensions are: 29cm*36cm*5.8cm roughly. I tried server and rack mounted PSUs, but only a single slot would fit and they are either below 250W or twice my budget. I think the best solution would be to get one or two external PSU like the ones that come with high-end laptops, and somehow convert it's single output power to PCI-e power pins. As my english is not my first language, I coulnd't find the proper term and google it. 
So the question: Is there any way to convert a laptop PSU to be usable in desktops, or should I just try to find some server PSU?
If I couldn't solve this, I'll ditch the whole project. 
Thanks in advance

[You_are_a_cunt]

laptop power bricks have a single fixed voltage output and all other conversions are done on the laptop's motherboard. Any idea what the case's model is?

[TheRandomness]

It's possible to use a laptop power brick (ideally a Dell DA-2, for 220W) as well as a DC-DC converter, such as the 160W one from HD-Plex, to power your PC.