This will not affect your application to university.
The PUM and the UMS are two different ways of standardising the reporting of examination marks. Cambridge International A Level grades are reported using PUM, while UK A Level grades are reported using UMS. As far as we are aware, only the University of Cambridge refers to PUM and UMS when making offers of admission to students.
The University of Cambridge recognises the differences between the PUM and UMS and has agreed this statement:
“The University of Cambridge recognises that PUM in Cambridge International A Levels are calculated differently from UMS in UK A Levels, and takes this into account when making admissions decisions.”