Laptop power supplies


Apr 29, 2014
Hi everyone,

I'm not looking to upgrade anything right now but i would like to understand how my laptop's power supply works. I've been getting into PC gaming over the last couple years and my curiosity about computer hardware has been growing along with my game library :)

The way I understand things (and feel free to correct me where I'm wrong) is that a laptop's power supply is that big ol' brick thing in the middle of the power cable. I've seen them come in 65W, 90W, and a few other options depending on your particular rig. I'm pretty sure I understand why an underpowered *desktop* will have issues (decreased performance, increased heat, greater risk of failure as certain components draw the limited power away from other things that also need it, etc.). But desktops don't have a dedicated battery like laptops.

So. Why would having too little wattage in a laptop's brick thing leave your laptop underpowered and at risk of damage/problems? Laptops always have a battery -- why does the cable that charges the battery make any difference if the components are all relying on the battery for power anyway? Shouldn't the battery be the deciding factor of how much power your PC can draw on while the cable simply governs how fast it can charge?

Thanks in advance for explaining this to me!


Oct 2, 2013
1.too little wattage would mean that while the computer is on and plugged in the battery would still be draining the battery to run (not very helpful)

2. in todays laptops the big old brick is only a ac to dc converter and inside the laptop there is still some power electronics to down grade that into the proper voltages to charge the battery and also down it to the 3.3 5 and 12 volt needed for stuff. for example my laptop uses a 20volt input to charge an 18 volt battery and downgrades all that to a 3.3v 5v 12v and somewhere between .6 to 1.3 volts for my cpu depending on its current speed.

3. even a battery can only charge and provide power at a set rate. charging it to fast will result in a fire or killing of the battery.

4. you have to remember that laptops are built for power savings in mind. a desktop cpu can easily draw more power then everything in a laptop uses together. for example my cpu can draw about 25 watts max while a desktop cpu (and better performance) can draw 100watts due to better cooling. though my cpu if I put it into a desktop could be rated for more power (and with that ive taken my amd a8 from 1.5ghz up to 3.0ghz) it cant stay there very long due to the small heat sink cant get rid of that 100 watts of heat.

and when it comes down to it when all them watts need to be cooled is really the limiting factor in a laptop because wattage of a computer is using is all turned into heat, light or sound energy. most of the wattage turns into heat.

when it comes down to it most of this may not make sense to you but if you learn about it then you will understand it. a lot of your questions goes into electricity and electronics and really is not computer dependent(could be applied to electric cars for instance). I suggest you just read to learn about it more.
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