Think of a power-supply unit (PSU) and, chances are, the rectangular ATX form factor, measuring 150mm (W) x 86mm (H) x 140mm (D), springs to mind. Larger-capacity models often increase the depth to accommodate a greater number of internal components, up to 210mm in some cases, but they fit into most enthusiast chassis just fine.

However, the PC industry has made a concerted effort to reimagine the desktop box into a smaller, sleeker package. Helping this ideal along are smaller-form-factor PSUs that are otherwise identical to their ATX cousins. Here's a list of common form factors in production today.