Not speaking from direct experience building a rig like this but the blog post mentions having 3 power supplies so the most direct solution would be to put each on their own dedicated circuit. As long as you have space in your electrical box this is straightforward to do though I would recommend having an electrician do the wiring if you aren’t experienced with that type of home electrical work.
Actually, putting each PSU on its own circuit is crazy dangerous. In the scenario of your suggestion, if one goes out, you are in for a fire. Highly recommend against that.
This might be one of those reasons why I'm not an electritian, but is it dangerous.
Back when I worked at a high-availability data center, all of our servers had dual psus, plugged into seperate circuits.
The transformer in the PSUs should electrical isolate the mains voltage from the low voltage side, so you aren't going to cause a short across the two circuts.
The only risk I see is a cascade failure, where the increased load on the second circuit causes its breaker to trip.
