XLSXMicrosoft Excel Open XML Spreadsheet
XLSX is well-known format for Microsoft Excel documents that was introduced by Microsoft with the release of Microsoft Office 2007. Based on structure organized according to the Open Packaging Conventions as outlined in Part 2 of the OOXML standard ECMA-376, the new format is a zip package that contains a number of XML files. The underlying structure and files can be examined by simply unzipping the .xlsx file.
XPSOpen XML Paper Specification
An XPS file represents page layout files that are based on XML Paper Specifications created by Microsoft. This format was developed by Microsoft as replacement of EMF file format and is similar to PDF file format, but uses XML in layout, appearance, and printing information of a document. It is, in fact, more justified to say that XPS is an attempt on PDF, but couldn't get enough popularity as owned by PDF for a number of reasons.