Now that we have covered 5 and 12 volt DC power applications over USB and Ethernet, this post will be about 20 volt DC expansion. This voltage is very common for laptops and Chromebooks/Chromeboxes. It is important to note that some name-brand manufacturers will have a third 'sense' wire in the power cable, to ensure that a no-name or incorrect wattage power supply is not used with their systems.
A good example is my Dell Precision 6500, which has a comparatively large (and more expensive) power supply for a standard-sized laptop/dock. A more-common Dell laptop power supply has the same plug, but I am warned that the wattage is not sufficient if I use anything other than the 210 watt unit that is designed for it. At 20 volts, that wattage means more than 10 amps of current, a phenomenal amount that I do not have the answer as to why the laptop needs so much (the battery, with nice LED level indicators, has always lasted me about two hours of use away from the dock).
I have an extra supply, that had its cord cut by my boss of the time, thinking that the unit was bad. As you've learned by now, I then think of ways to put it back into use. You should also know that I have too much of my Dad's blood in me, and that we never thrown an item away in the hope that we can fix it later.
My ASUS Chromebox in the office is also 20 volts DC, a power supply that is half as large. It has a very-common 5.5mm x 2.5mm (the same dimensions of the power plug for older Roku units) plug for power, without any 'sense' line. In addition my Lenovo 11e Chromebook and my wife's Lenovo convertible laptop/tablet also have 20VDC power supplies, a fifth of the size of that of my Precision. I have an adapter plugs set that I should have covered in earlier posting, in that they have the common 5.5mm x 2.1mm jack inputs, and convert it into all of the plugs I will use on this project.