Another solution I have found for this in other forums, is to clean out the dust and accumulated crud from your PowerBook motherboard and internal fan.
This improves the cooling efficiency. Over time the Mac gets full of dust and can't cool so well.
This should be done very carefully, there are a bunch of YouTube videos about this.
You also need to buy a special screwdriver. This is called a 1.2 mm pentalobe, there are lots of these on eBay for a few bucks. You need one of these to remove the back because Apple use a special kind of screw that no-one else in the world uses, specifically to prevent you from doing anything to your PowerBook yourself.
Do not do this unless you are comfortable with this kind of hardware task.
From the searches I've done, apparently this will not void your warranty, but if you are worried about this, ask your iStore.
This is in addition to using the fix of using right hand ports as described above, which clearly solves the problem.
It doesn't apply to newer laptops unless they have been used in a very dusty environment.