Take the 2-minute tour ×  Have a 40W power supply - will it
power a laptop that needs 65W?  I know that the basic
calculation, voltage x amps = required wattage, so 18.5v x 3.5A
=65W  I realise that it should only draw the power it needs, but
in practice, will it damage anything? Can supplying not enough
power cause problems?  Bottom line is, I'm trying to under-power
the laptop.....  share|improve this question It really depends
on both the power supply and the machine in question. My rule of
thumb is to not load a power supply over about 75% of it's rated
max. So, you're pretty far over. I'd like to think the worst
case situation is you burn out the PS pretty fast, but if it's a
crappy one you could damage your laptop. Unless you like
breaking things, I suggest you just find a bigger PS for that.
Also, I think you mean 'power brick' as your laptop should have
part of a regular power supply within it.. –  Doc Sep 27 '11 at
19:58 Thanks for the quick response.... you pretty much told me
what i suspected - was