The (legitimate) manufacturer will be able to tell the difference and won't service or provide support for counterfeits. And warranty claims are obviously out of the question.

It matters when it catches fire because they saved a few cents skipping some failsafe in the power supply.

You are right: https://www.youtube.com/watch?v=fSE_Nm7pAw4 - this video from bigclivedotcom shows the unique failure of a usb-c power supply that also took out a MS Surface and associated monitor with it.