Computers are electrical appliances that require a steady stream of 5V DC to operate. Just one problem: Electricity is supplied in a very different format to your home. In the United States, this is 110V A/C. (Other countries offer 220V A/C. Wikipedia has more on this.)
So every computer has a part called a "power supply" that converts the household current into the type the computer needs to run. It also provides 12 volts for hard drives, and 3 volts for other accessories. All in the direct current format that the electronics need.
There is some inefficiency in all transformation. Some of the electricity's energy is lost to heat when slowing the voltage and switching the style. Powering one personal computer, this is no big deal.
This becomes a big deal when operating a datacenter. In datacenters, you have thousands of computers, consuming megawatts of energy, and each has its own power supply to switch current. The heat is immense, and air conditioning is required if you live in a milder climate than Canada in the winter. (Canadian data centers can forgo air conditioning between September and April.)
So for datacenters, I think we need to move from individual power supplies to a collective DC converter that provides hundreds of strands of 5V, 3V, and 12V, each with the proper cabling, and each bundled so that we can shut down one particular computer without shutting down the others. Sometimes we have to do that. This one unit will convert the power more efficiently than individual power supplies by economy of scale. Less energy is lost to heat, and less heat needs to be pumped outside the datacenter. Considering that the average datacenter uses 10MW of electricity, this should provide considerable savings. Moreso because air conditioning uses lots of electricity.
The only reason that this isn't being done now is economy of scale. Lots of people have personal computers, so individual computer power supplies are cheap. Getting a collective power supply now would be expensive because it would have to be custom made, but if enough people put them in their datacenters, the price would plummet.