Despite that above says:
"Currently the following character encodings are supported by the mbstring module. Any of those Character encodings can be specified in the encoding parameter of mbstring functions.
The following character encodings are supported in this PHP extension:
[...]
Windows-1252 (CP1252)
"
"Windows-1252 (CP1252)" is an invalid as an mb_convert_encoding() encoding parameter value.
"Windows-1252" is valid.