It isn’t a regulator, it’s a charger - depending on the design, you can get even higher voltage spikes. 12V batteries charge at 13-14V, but most chargers design for lead acid can get away with reallly really noisy voltage transients due to the way lead acid works. It’s a pretty insensitive chemistry and dampens them normally.

Some chargers with ‘equalize’ or even worse ‘desulphation’ can intentionally go even higher in voltage than normal charging voltages.

So basically ‘if you just assume it wouldn’t kill your laptop to directly connect it, you’re playing Russian roulette with your laptop’.

With a decent spec sheet (and oscilloscope) to verify nothing too crazy that the charger is doing, some decent power filtering capacitors, and good DC-DC power supply you’d be fine though.