Hard to tell from the pictures.
Take your multimeter.
Disconnect outputs from your power supply. Set it for about 10V.
Measure from + to - and tell us if it's 10V or 20V.
Measure from gnd (earth, the centre banana socket) to + and -.
Is there any voltage from ground to either? If so, how much?
If it's as I *SUSPECT* it is, you'll have 10V + to -, and nothing gnd to + or -.
If thats the case, you should jumper gnd to - in this case.
(Many of these power supplies had a solid jumper link installed between the banana sockets)
Now take your multimeter. Make sure the CRO and power supply are plugged in the same outlet.
Measure from power supply gnd/- to CRO ground. There should be no voltage.
Check from power supply + to CRO ground. There should be 10V.
Check ohms from gnd/- of the power supply to CRO probe ground. Should be under an ohm.
If that's all as indicated above, then you have a "normal" setup.
You CRO probes ground can go to the "ground" (0V) part of your circuit *ONLY*
If you're in doubt, you can connect a 10R in series with the cro probe ground to wherever you intended to put it.
10 ohms won't make any difference to the CRO readings - which should have a minimum input impeadance of 1M, and probably 10M. But if you try to "earth" to something that's 12V or more away, your 10R will smoke rather than the CRO.
(I once installed such 10R resistors in the little ground wire from the probe, when students kept blowing sh!t up)