different cables to power laptops

Factual Questions
1

Are my assumptions about a standard cable powering a laptop below safe? I have two cables with slightly different transformers but the jack is the same on both and was wondering if i could interchange the cables.

Laptop A comes with power cable A that has transformer Input: 1.5 A and Output: voltage 19.5 V and current 4.62.

Laptop B comes with power cable B that has transformer Input 2.5 A and Output: voltage 19.5 V and current 6.7A.

If you plugged cable B in to laptop A it will only draw the power it needs and no more. It will pull a current of 1.5 A on the input and 4.62 A on the output which is under what it is designed for. So this is safe.

If you plugged cable A into laptop B it will try to draw the power laptop B needs and will try and pull a current greater than the 1.5 A the input is designed for. And the output of the transformer will not be designed to carry currents greater than 4.62 and the laptop will try and pull 6.7 A. So this is not safe.

Is that right so far?
Or is it safe to use cable A on laptop B.

Also if the voltages were different could you just use the power rating? As in, multiplying V * I and see if the cable is capable of the appropriate power?

As I’m thinking now as well I’m wondering does laptop B only pull its maximum current if all the parts were in use(hard disk, the ram part operating several programs, reading a cd and connecting to the internet etc)? Which could mean you could plug laptop B in with cable A and it wouldn’t pull a current greater than it was designed for if you were only using a word document etc.

2

I’ve switched Gateway power supplies around. You want the output voltage to be the same, and they must have the same polarity; the picture showing the center pin to be positive or negative.
A PS rated at a lower current will charge the battery, but will very possibly overheat and fail if used to power the laptop for an extended period.

3

You might get a way with the A power supply on the B laptop for a little while in an emergency. It will run very hot and they sometimes run hot anyway. There may be some screen problems. Eventually, the A power supply will buy up. It’s not a wise substitution for the long run. The other way around, with B power on the A laptop, you could go forever.

If the battery is good on laptop B, you could cable up the A power supply and just let it charge the battery without turning on laptop B. When charged, pull the power supply and live off the battery. The should be safe and effective.