My regarded-as-moderately-high-end US electric kettle isn't really any faster to boil water than my stovetop is—but, it can hold a temperature, and has several settable stop-and-hold-points at sub-boiling temps, which is great for various teas and coffees.

What's not relatable to me is European (I assume?) reports of boiling water in an electric kettle, then transferring to the stovetop. My kettle's not meaningfully faster than the stovetop, and is a lot slower for quantities past a liter or so—it's only worth having for the other features. I assume that's the voltage difference making itself known.

Yes: I generally only fill up a kettle in the 500-750 mL range if I'm only making one cup, and it generally boils fast enough for my tea.

> How would this boil water faster if it’s still the same wattage?

It wouldn't be the same wattage: it would be double the wattage.

The wiring can handle 15 or 20A, and at 120V that's a practical limit of 1800W. You keep the amperage limit (no cabling replacement needed), but 240V would allow 3600W.