Hi,
You could create a custom report in ServiceDesk Plus to get the list of all the PO's.
Login to ServiceDesk Plus, go to Reports > New Custom report, choose tabular report, select the Purchase module and proceed to report wizard.
Choose the required columns and run the report. You could export to results to a html, pdf, xls or csv format, with the options available to the top right hand side.
Regards,
Stephen