>run it from a different circuit but the same utility power.
If you're going to come from a different circuit, see if you can at least pull it from a different phase, if we're talking a 120v circuit on 240v service (typical US home service). It's a small improvement, but I'd say 10%+ of the power outages I've seen have been just a single phase going out.
The center tapped transformer that provides residential split phase 120/240 on its secondary winding connects to just 1 of the 3 grid phases on its primary winding. If that one phase goes out on the grid, both sides of the split phase service go out together. There would need to be a fault on just one side of the split, downstream of that transformer, for your suggestion to hold up. Certainly not impossible, but far less common than a "losing one phase" scenario which would typically originate upstream on the high voltage side.
On a commercial 3 phase service, yes, connect redundant PSUs to separate phases, since each phase on the panel actually corresponds to each phase of the grid.
> The center tapped transformer that provides residential split phase 120/240 on its secondary winding connects to just 1 of the 3 grid phases on its primary winding.
I believe that's a USA peculiarity. Where I live, the usual residential and commercial wiring is from 13.8 kV to 127V/220V through a three-phase delta-wye transformer, in which the primary connects between each pair of phases, and the secondary connects between one phase and the neutral (the high-voltage primary side does not have a neutral). When one phase of the high voltage side is lost (very common, since each high-voltage phase is a separate wire and has an independent fuse upstream of the transformer), what happens is that one phase of the low voltage side stays normal (the one between the two intact high voltage phases), and the other two have a lower voltage which varies depending on their relative load.
Look up Wye vs Delta; but the basic point is in delta the phases are connected in series with each other, and in wye they are connected in parallel. It's easier to visualize when you can see the tap points on the transformer secondaries though.
You can definitely loose one phase of a split phase transformer. I've seen it 3 times in my life. Sometimes it is completely out, other times I've seen only getting 80v rather than the full 120.
Agreed, as I said it seems like around a 10% improvement, which considering it's fairly easy to ensure the circuits are on different phases, is worth doing IMHO.
If you're going to come from a different circuit, see if you can at least pull it from a different phase, if we're talking a 120v circuit on 240v service (typical US home service). It's a small improvement, but I'd say 10%+ of the power outages I've seen have been just a single phase going out.