Toby I believe what you want is your little charger to be as regulated as a car alternator. Is that correct? if so,
Car batteries are designed to charge at 14.2V all day. then capacity at rest is 0~100% from 11.6 to 13.6V approx. ( 2V range)
Cheap chargers are simply full wave rectifiers that give a charging voltage at rated current. Of course with no load (fully charged ) that voltage may exceed 14.2 and start to boil off acid electrolyte. 14.4 is marginal, 14.6 is excessive. I need your specs to define the best solution. Power and voltage or P/N.
That means you need a voltage limiter.
For small power you can use a series regulator LDO type, but if the drop is excessive > 0.2V? a shunt regulator to drop the peaks of the full wave source.
For large power, phase controlled SCR's are more efficient,which Lambda used in their early linear high power designs.
Like @steveh said, if it just a trickle charger (1A) TVS might seem to work. But if you examine the specs closer, they have high ESR which means for automotive use, they may trigger at 13V and clamp at 19V. Also the Reverse voltage rating of 10V means if you dont protect it, it will blow if someone charges your car with the jumpers reversed momentarily.. Thats why all car electronics are designed for +28V/-14V MINIMUM.
So I would suggest a more accurate solution.
Any band-gap reference diodes @ 2.5V such as found inside LM317's are accurate within mV's. But LM317 has excessive drop voltage of 2.5V. Even an LDO regulator like the LM2940/LM2940C 1A Low Dropout Regulator is no good with 0.7V drop at 1.0Amp. So a shunt regulator like a TVS but more accurate would be best, using cheap TO-220 power transistor and Band Gap ref voltage. Normally it takes a dual common emitter transistor, ref. voltage and resistor ratio to make an "Active Load" as we call it in the industry. THere are many approaches. Keep in mind the car alternator if out of adjustment on the high side may blow your charger regulator if under the hood. So it has to consider that too. If that is the case. then a series cut-out switch is best. PNP series pass rated for 10Amp with driver set to 14.2V - 0.6V = 13.6V zener or (13.6V drop with active reference.) to trigger NPN driver to PNP series cutout protection. Total cost a few bucks.
Need more details?
Which do you prefer. What's your budget?