The problem is that this repeated conversion between AC and DC at each stage results in a 2–3% power loss per step. Across the entire system, this cumulative inefficiency is significant. NVIDIA is seeking to overhaul the current structure by proposing DC-based power design from the supply stage as a way to reduce these losses.
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That summary is really oversimplifying the situation. It's not that “DC means less conversions”. But rather, that data centers run everything off of UPS's, which inherently force an AC to DC to AC conversion if the servers are powered by AC. And even that is only true if we use specific types of UPS's that run power constantly through the UPS. There's other types where the UPS only is switched into the circuit on power failure that could eliminate that conversion loss, at the cost of creating a brief power glitch.
Finally, 800V DC is a scary beast to work with... It's much harder to interrupt the flow of high voltage DC; in AC the voltage periodically goes to zero, giving an opportunity to extinguish arcs much more easily as the arc inherently stops briefly many times per second.
How much efficiency can be gained overall?
The article mentions 4 conversions à 2%-3%. That would be like around 10% or something. But idk for sure if it can be calculated like that or if other components in the electricity stack would change as well