A major goal of Luggable PC (Mark I) was to use components I already had on hand, which meant a full-sized ATX power supply unit (PSU) because I've never bought anything else before. For Mark II, I'm opening up the project budget to buy a compact power supply for the system.

There are plenty of small proprietary PC power supplies available in the aftermarket but low-production items will have limited selection and may be difficult to replace. The only units that were remotely interesting were the PSU for high-volume small form factor PCs of large manufacturers like HP or Dell. But they tend to be low powered units rated at 250W or less and also lack the power plugs needed to feed a power-hungry full size GPU.

So I started looking at the standardized PSUs. In the ATX power supply specification I found online (revision 1.31 dated April 2013) I learned there was a significant step in the evolution of ATX power supplies that shifted original focus from the 3.3V and 5V rails over to the 12V rails. This explains the "12V" suffix on some of these specifications - when a manufacturer names their ATX PSU as a "ATX12V" power supply, they declare 12V focus on power capability.

However, the first three letters still describe the physical form factor. I didn't find many CFX12V or LFX12V units available. TFX12V and FlexATX12V are more common but they are equivalent to those HP/Dell PSUs with low wattage rating and no PCI-Express card power plugs. We want something smaller than ATX12V, so that leaves SFX12V.

Thankfully there seems to be a healthy SFX12V niche in the ecosystem. They do tend to be lower in power rating than full sized ATX12V but I expect 450-600W to be plenty. And they have most of the power plugs of a full ATX12V unit, including those valuable PCI-Express power plugs.

The power plugs actually present a bit of a problem: any wires I don't use in my system is dead weight and taking up space. In theory this can be resolved with a SFX12V PSU with modular plugs and wires. I ended up getting one modular (Corsair SF450) and one non-modular (FSP Group FSP450) SFX12V PSU to experiment with.

On the physical form factor specification, SFX12V was only a few centimeters smaller in each dimension relative to ATX12V. But those numbers understate the reduction in physical volume. When I pulled them out the box I was quite pleased at how compact they were. This is going to be a tremendous help in keeping Mark II slim.

[caption id="attachment_9745" align="aligncenter" width="1022"]IMG_5201 ATX12V and SFX12V power supply units side by side illustrating difference in volume.[/caption]