if you use 1.24 volt, you need more electric current (W). i read about this long time ago, but i forgott it.
the thing is that i found a Xps m1710 power supply on internet for 40 euro, but it wasnt a Dell product, (it was a copy, and they can be very bad for your laptop (if you have bad luck), my friend bought a copy power supply to his laptop, the supply puched to much Voltage to his laptop, and something got bad.
for me, its worth this 20 extra euro, to get a Real Dell Xps m1710 130 W supply.
you feel a big differnce when you overclock with 130 W instead of 90 W.
this is going to be fun....he he