The HP's power-supply is 19.5V:

js2 • yesterday at 11:20 PM • 1 reply • view on HN

The SD-500 is available in 12V, 24V, and 48V, none of which adjust to that range:

Also, not sure why you're suggesting a DC-DC supply here? His input is AC.

a96 • today at 6:57 AM

Probably the idea is to have one big AC-DC PSU and then separate DC-DC regulators for each box from that rail.

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