It sounds like you tried to power the servos from the Arduino 5V pin while powering it
from 12V on the power jack.
Two things wrong with that: firstly the on-board regulator cannot handle that much
power when dropping 7V, secondly you shouldn't be powering servos or motors from
the 5V logic supply in the first place, but use separate 5/6/7.2V power for the servos
(6 and 7.2V are traditional servo power supply voltages, note, not 5V, so some servos
may have issues with only 5V too).
You were lucky you didn't damage the Mac's USB port in fact.
Motors and servos often put voltage spikes on their supplies - this can destroy logic chips,
or simply make them misbehave and unreliable. Separate power for motors and logic
chips is a very very good idea.
Budget at least 1A per servo for small servos, more for larger ones.
Your Arduino's on-board regulator is probably toast, it may have taken the whole board with
it if you are unlucky, or it may still work from USB (use a powered USB hub though, to
protect the Mac from it).