A DC system is, in theory, more reliable because there are fewer components and, therefore, fewer stages of voltage conversion. The system is more energy efficient because less power is lost at the conversion stage.

Currently, the UK power supply is progressively stepped down to 230V of AC power in the building. This then has to be put through a UPS that converts it first to 30V AC, then rectifies it to 500V of DC, then converts it back to 230V AC. So the power has already been through two conversions even before the server PSU switches it to 12V DC on the system backplane.

With DC, you can rectify the mains supply once to 30V and feed it straight into a bulk DC to DC converter that feeds individual, specially adapted servers at 48V, thereby eliminating one of the conversion stages and delivering energy savings.
The natural state of DC evolution is in the telecoms world, which has always used 48V equipment and where failures do not happen that often.

People are dismissive of DC because they are unfamiliar with it. Most people in the UPS world do not know much about DC, and vice versa. There is not much empathy on either side but I think that will change.

I expect to see the first commercially operating datacentre based on DC power rolled out in the telecoms world within the next 12 months, with other industries following once the technology is proven.