Looking for an active pen compatible with Precision 7680 OLED Touchscreen

Not possible.  The system has a touchscreen -- not an active display panel.  It will work with a generic capacitive stylus, but won't have support for an active pen (it won't support high precision drawing or pressure sensitivity).

If you need those features, they're available on some 2-in-1 systems (all of which are Inspirons, not XPS or Precision models).