Try this variant on for size:
One time setup:
Export your data to CSV
Start Excel, do File, Open and choose the CSV file
Save it (making sure to force the save as CSV ... accept the defaults, in other
words)
Select the data you want to chart and do Edit, Copy
Switch to PPT, add the chart activate it, choose Edit, Paste Link.
Your data will appear in the chart's data sheet and will now be linked to the
CSV file.
After setup:
Edit the CSV file (or presumably create a new file, same name, different data)
Start PPT, open the presentation and doubleclick the graph to force an update.
Yep, the charts won't update until you activate them. There are macros to get
around this, but it might be better to create the charts in an Excel file on
chartsheets and copy/paste link those into PPT. If you can work out how to
link the data for Excel charts to a CSV file, that'd probably work better, as
the charts would update automatically when you open the PPT file.