Custom External Power Brick?

[JavascriptCodingGuru]

I'm trying to build a super small, but powerful, gaming pc. I'm building a custom case and I would like to have a external power brick. I've looked and looked for something and I can't find anything so I have come here to ask for help. I'm looking for something that can do 400-500w. Power consumption will be lower but I would like some breathing room.

 

[Aeacus]

Here's a reason why there's no external PSUs for desktop PCs,
link: http://www.tomshardware.co.uk/answers/id-2405162/external-desktop-psus-real-thing.html

As far as building a small footprint PC, rather than using standard sized ATX/PS2 PSU, use SFX PSU which is considerably smaller. E.g Corsair SF series,
450W specs: http://www.corsair.com/en-eu/sf-series-sf450-450-watt-80-plus-gold-certified-high-performance-sfx-psu-eu
600W specs: http://www.corsair.com/en-eu/sf-series-sf600-600-watt-80-plus-gold-certified-high-performance-sfx-psu-eu

Here's also a good image to show how much smaller the SFX PSU is compared to the ATX/PS2 PSU,
image:

With SFX PSU, you can use much smaller cases, known as HTPC. E.g Fractal Design Node 202,
specs: http://www.fractal-design.com/home/product/cases/node-series/node-202

 

[JavascriptCodingGuru]

I appreciate the answer. I found something that is pretty cool if anybody ever finds this thread in the future. It's not a custom external power supply but it's a really really small internal power supply. http://www.hd-plex.com/HDPLEX-400W-Hi-Fi-DC-ATX-Power-Supply-16V-24V-Wide-Range-Voltage-Input.html.
HDPlex 400w. Goes inside the case but it's really really small, smaller then a sfx psu. Has everything you need including a 6+2 for a gpu.