AS-EE
If your that worried then don't even use the charger that came with Hot wheels of for that matter any charger like that because they work the exact same way. There is only a transformer and diodes with nothing more. Also throw away your old sears charger as they do not regulate either.
Umm the final output voltage if you know what math to apply to center tap full wave rectification is at .636(15v RMS/(Sqrt 2/2) - .7v) = 13.0464 volts CONSTANT
Plus 10% = 14.3 volts. Minus 10% = 11.7 volts and your charger just stopped working. Not quite the constant voltage in bold letters that you used to reply to Rodney. Sorry you've just lost all credibility from me. I gave up Hot Wheels a long time ago. Any engineer worth his salt worries about line voltage variations.
My Sears charger is an automatic taper charger and contains more than just a transformer and two diodes. Even the most basic chargers you are alluding to contain a circuit breaker as well. You are starting to sound like a young man defending his turf at all cost. Don't you worry about someone copying something you've incompletely posted on the Internet and hurting themselves?
Most well designed commercial chargers now use a switching power supply rather than a full wave design. The switching design has gained favor because you don't need that huge hunk of iron transformer and they taper the charge as well as the voltage to suit the battery. This increases the life of the battery.