Can be fuses be replaced by PPTCs as the main overcurrent protection for AC Power Supplies inputs?
The fuse is an integral part of a switched mode power supply in an installation. It's there to protect the wiring in the building's walls from melting and causing a fire should the SMPS develop a short circuit fault.

Fuses have to meet a high degree of reliability when they go open circuit and they can deal with voltages present on the AC line that a polyfuse won't i.e. a fuse won't bat an eyelid should a spike of 600V come along. A polyfuse might melt shut and therefore offer no further protection.

I'm sure there's a possibility that someone has made a range of polyfuses that work as reliably as a standard fuse so keep looking - none of those listed by mouser appear to fit the criteria required of a conventional fuse.