The world's smallest ATX PSU

We're partial to Seasonic's power supplies but 600W units - or even 450W units - are overkill for most fanless builds. HDPLEX launches this 250W fully passive PSU using reliable and highly-efficient GaN (Gallium Nitride) components. The compact 170 x 50 x 25mm PSU achieves 94% efficiency at full load and can be synchronized with a second unit for a 500W PSU if needed. The automotive-grade HDPLEX 250W GaN Passive AIO ATX power supply comes with custom cables, and will be available in the coming weeks. 

Source: HDPLEX