iPhone 13 pro max charges up to 80% only no matter how long it is plugged in.

I have got my iphone 13 pro max a month ago. Got the 20 watts adapter with it. I have been charging it on the new apple adapter. It charged to 80% and then stopped no matter how long it was plugged in. At first I thought it is a battery protection thing from Apple and turned off the optimize battery charging feature, still it didn't charge up to 100%. Then I used a Samsung 20 watt adapter and it charged it to 100%. I want to find out if the adapter is a real Apple one or a fake one. I tried to find the product with the serial number on Apple support and could not find it there as well. Is it possible to find it with the serial number?