Actually there isn't any service to read XLS files, to read it out-of-the-box with TW, the file should be a CSV file or a simple TXT file.
Please refer to following Thread for more details on loading the csv: How to load data into a grid from file repository which contains an excel file?
For details on Bar chart please refer to following link: PTC Bar Chart Widget
If you want to import Excel file; you have the option to create your own Extension.
I hope it helps.