Power Architect comes with jdbc driver for postgreSQL.(you can find it under jdbc_drivers folder of power- architect). check the user preferences. see the attached screenshot for this.
To create a new connect right click on 'PlayPen Database' >'Add Source Connection' >'New Connection' in a left panel.
select Database Type as PostgreSQL, see the attached screenshot for more information.
After filling all information click on test connection. Hope this help you.