Frequent battery replacement?
Seriously, In the context of charging power, Porsche's constant mentioning of their 700 V voltage has relevance only for the thickness of the charging cable.
The fundamental issue is that for the given battery size, tripling the charging power (relative to Tesla's current Supercharger), triples the C-rate which is detrimental to the long-term health of each cell.
So maybe Porsche is betting that owners of the Taycan will not mind the more frequent replacements (or upgrades) of the battery pack...
That's one of quite a few possibilities. First, two earlier possibilities that has since been ruled out:
* High power-density cells: Porsche has made it clear that they're using high energy-density cells (if I remember right, it was something like 260Wh/kg).
* They only plan to allow 350kW very briefly (contradicted by their overall charge time announcements)
* The vehicle is super-inefficient, and thus it achieves its range with via a gigantic battery pack (this does not appear to be the case)
Now for the others (may be a combination of several):
* Porsche has access to some unique cell variety beyond the state of the art that everyone else in the industry has access to, or some charging "trick" that nobody else has figured out (exceedingly unlikely)
* Porsche is deliberately frying cells with a high C rate (accepting the cost to replace packs on warranty from those who do 350kW charging often, counting on such people to be in the minority and having a large enough vehicle profit margin to eat the cost)
* The actual pack capacity is much higher than the usable capacity, so what looks like a high C rate is actually a more moderate C rate from the cells' perspective (that is, large chunks of the pack locked off on the bottom and especially the top). This will also make the wear on the cells less (charging near the centre of a cell's range causes less degradation than near the extremes).
* 350kW will be available in a variant that comes out "in the future" (such as the "Cayenne Turbo" to go with their "Turbocharging Network"), with the intent to take advantage of several years more of cell tech advancement.
* 350kW will be only available in variants that use a double-thickness / super-long-range pack, akin to the Roadster (Porsche has not announced plans to make such a version, but since we know little about the differences between the Cayenne variants, it's a possibility)
If I had to guess, it's a mix of "burning out cells with a high C-rate", "significantly higher real capacity than usable", and possibly "350kW only in future variants" (either for chemistry improvements or super-long-range packs).