Solved! can i use 240w ac adapter instead of 150w ?

Solution
Why not? There is not any problem if a power supply has more wattage capacity!! The device would draw the wattage it wants... Check only the DC output voltage to see if it is the same with your device / battery (e.g. 19V).
Why not? There is not any problem if a power supply has more wattage capacity!! The device would draw the wattage it wants... Check only the DC output voltage to see if it is the same with your device / battery (e.g. 19V).
 
Solution
Generally Dell and Alienware laptops will refuse to charge if it does not recognize the charger as genuine, a bit of Keurig-like DRM reminiscent of ink cartridges, but pitched as a fire safety measure. So it should not hurt anything but may not work.