with a 1024 x 768 resolution and 32-bit color set on the monitor (does that matter?)
but how do I check my stencil buffer format?
Good question. In my case I have modified version of DefaultGLCapabilitiesChooser with DEBUG = true (check the source). If you don't want to rebuild JOGL, just make your own copy of GLCapabilitiesChooser similar to DefaultGLCapabilitiesChooser and pass it to JOGL when creating GLCanvas.
And sry but what is VSYNC swap buffers synchronization?
This functionality, if enabled, causes every call to SwapBuffers [performed internelly by JOGL just after display(...) call] to wait until next vertical retrace, so you can conly see complete frames on your screen.
Now imagine you have flat panel w/ 60Hz refresh and your app renders 58 fps. With VSYNC enabled you get exactly 30 fps just because of rendering is too slow to fit one frame period (1/60 s) and you are missing every second frame.