Setup approx V/div and timebase settings and connect the scope probe to the powersupply.
Set the scope to single shot capture mode (trigger menu / sweep --> single)
Adjust the trigger level to say 0.5V above ground so it triggers as soon as the voltage rises (the knob labeled level)
Check that the top right button is green indicating it's waiting for a capture event (If it's red press that button to reset for another trigger event)
Turn on the powersupply
The scope should single shot capture the waveform and then stop (red led)
To repeat, turn off the powersupply, press the red button (so it turns green) and turn on the powersupply again