The lower figure of 20W is pretty standard: go take a look at the battery in your laptop. Most Dells are 65Whr batteries - ie. 20W for 3 hours of battery life (

The lower figure of 20W is pretty standard: go take a look at the battery in your laptop. Most Dells are 65Whr batteries - ie. 20W for 3 hours of battery life (to a first approximation, LiIon is a bit more complicated than that). The ubiquitous small form factor PCs like the Optiplex 780 (http://www.dell.com/downloads/global/corporate/environ/comply/optix_780_dccy.pdf http://www.dell.com/downloads/global/corporate/environ/compl...) use a 235W (max) power supply, which will be overspecced to trade off failure rates for manufacturing cost. Those machines actually draw less than 150W flat out. And they're everywhere. A certain large e-tailer with an emphasis on frugality used to use them as developer desktops(!). Who knows what's in a typical consumer beige box, but it isn't pulling 500W continuously, unless they're playing, say, Skyrim 24/7 with a big graphics card - in which case of course one would specify the correct (safe) component for the design. I'd argue that they're not typical by that point; most people won't spend £300 on a graphics card (I do).