Yes, the US Military is likely the greatest logistics organization in the history of the planet, and manufacturing would be prioritized.

And sure, THEORETICALLY, we could install mitigating tech to instantly disconnect each transformer the millisecond induced over-currents are detected. But in REALITY power companies are insanely tech-backwards. Even today, in a major developed area like around Boston, the technology for DETECTING outages is [wait for customers to call in] and [drive a crew out to look for a break]. Last month, there was a storm that caused widespread outages in much of Maine and NH. Crews were in for over a week, brought in from over a 1000-mile radius; I personally was up there and saw convoys of crews from Tennessee, Pennsylvania, Canada, etc.. It took over a week to restore power in just that region, with zero shortage of supplies. They rely on mutual-aid cross-covering regions to get things working again. In a global-scale event, EVERYWHERE is down at once, and the crews are each on their own.

I had to call in repeatedly about a serious undervolt situation (99V-103V) that persisted for hours and was damaging equipment, and they had no clue about it. They are not even installing technology to detect outages; they sure as hell aren't spending money to mitigate them.

Now, seriously consider a Carrington+ event or EMP attack. The reasonable assumption, even with the mitigation tech you promote, is that almost nothing works. Perhaps a few zones got disconnected in time, but no grid.

This means the entire population will have to survive on the available stock of just-in-time fuel, food, and other supplies.

Most vehicles will not work. Only pre-1980s vehicles and vehicles stored well underground or in basically Faraday cages will work. Charging systems won't work. Fuel pumping stations won't work. So, we've got manual pumping for single-digit percentages of working vehicles, which need to deliver remaining food stocks, and all the equipment for your manufacturing effort.

Most telecomms do not work.

What's in most people's refrigerators will last a few days. Skip a few meals and civil disorder starts. There are at most a few weeks before serious starvation and civil unrest starts.

Now, under these conditions, you propose to gather enough people to:

1) design these new models of transformers that are easy-to-construct-but-still-work-in-modern-systems,

2) determine the logistics of finding factories that can work, getting those factories working, and sourcing material,

3) moving that material to those factories

4) obtaining, moving, watering, and feeding the people to man the factories,

5) actually building the transformers,

6) distributing the transformers to where they are needed.

7) FINALLY, we can get to work rebuilding and cold-starting the grid

There is no way even in a Polyanna++ optimistic scenario that this will work within three-six weeks.

By the time even some of the first 3-5 steps are completed, much of the population will have passed the starvation window of a few weeks, and that is assuming no ad-hoc local wars, and that it wasn't an EMP attack as the start of a war.

In contrast, spending only about $500 million on a reserve inventory of transformers, pre-cashed in appropriate locations, we can jump directly to step 6 or seven on day-2.

Even under the pre-stocked transformers scenario, it's unlikely that everything could be restarted in time to prevent serious follow-on societal-scale damage.

Plus, since each transformer would need to be disconnected (it's the length of attached lines that generate the damaging current), will the cost of building and installing mitigation devices on every transformer, and a system to operate them, actually be cheaper than building spares? It actually seems like and warehousing building spares is likely a cheaper option.