Oh I forgot to mention there is a wall outlet rf noise filter on the scopes chassis. I was thinking do I need to be connected thru this point to get accurate measurements. Here is another pic
No, that's just to prevent electrical nose produced by the power supply from leaking out, for testing purposes you can ignore that filter and power the supply directly.
In regards to your other question NO, absolutely do not try to feed these with a lower voltage. I tried powering one of mine up on the bench with a series bulb to limit the current and it blew up, I then had to spend more time repairing that new fault before I could get on with the rest of the project. Do not under any circumstances try powering it with a voltage outside of the 120 or 240V it is rated for.
For a load I used a 21W automotive light bulb, the sort of thing that is/was commonly used in brake lights. To connect to the power supply I used alligator clip leads clipped to the correct pins, using the LeCroy schematic for reference. You have to use the DC ground pins on the output connector, don't try to use earth ground.
Honestly if you are a beginner this is not really a good project. Switchmode power supplies are dangerous and notoriously tricky to work on and this one is a particularly difficult one. I have many years of experience repairing gear and I struggled with these quite a bit before I figured out the issues and fixed both of mine.
Oh and the LeCroy schematics, I don't know if they're full of errors but they are definitely for a different version of the power supply. The PCB is identical but some of the components are different in order to make some outputs the opposite polarity of what Tek used. This sort of thing is/was fairly common with a power supply like this, the OEM had a series of different base models to offer and then the customer could select customized variations of these, choosing the output voltage(s) and polarity and other optional features. LeCroy and Tek both used the same OEM but specified the configuration differently.