Got a 20000mAh power bank rated :
input:DC 5V/2A 9V/2A 12V/1.5A
output: DC5.1V/2.1A MAX 3.6A
went to vietnam (which is apparently operating on 220V 50Hz) and used an international travel adaptor which has an inbuilt usb port. Plugged my usb cable into the international travel adaptor usb port to charge my power bank but it fried my international travel adaptor.
Anyone with good electronics knowledge know why?
Vietnam and Australia have the same voltage (roughly), it shouldn't have needed to transform anything at all. Most things can handle variations between 220 and 230v
The majority of batteries are not designed to charge at hundreds of volts. For example, the highest input voltage of OP's power bank is 12V. Phones generally charge at 9V. The conversion has to happen somewhere.
You missed the part in OP's description where he says his international travel adaptor has USB ports on it. That's where the conversion is happening.
Which "international travel adaptor"? A brand name, or a no-name? Had you ever used it before, or was this the first time?
if i charge my power bank via my laptop, it will be trying to get 9V/2A from my laptop. Most laptops usb give out 5V/1A. will this power bank fry my laptop.?
You really need to give specifics. Which brand and model of what?
its an outdated MI power bank with the input output specs above. laptop is Dell Latitude 3520
Why do you say it will try to get 9V/2A? The specs you gave also states 5V/2A.
It won't fry your laptop, it'll just charge at a slower rate.
@Thenarrator: 5V/2A is the maximum the powerbank can take. If your laptop gives less than 2A it is OK, your powerbank just charge at a slow rate. It cannot force your laptop to output 2A.
And the 9V and 12V input are quick charge that only happens if you have a charger that support them.
possibly something to do with transformers and changing the voltage from the supply voltage to the desired voltage. This is usually done in the power brick but since you plugged directly into the adaptor instead of plugging into a brick (the charger plug part), it fried.