Thanks for the great response. Regarding safety, I have found it difficult to find any sort of safety procedure for working on power supplies. Dave mentioned discharging using LoZ on a DMM but I'm not sure what I'm discharging. Is it the transformer? A certain capacitor?
If you're working unplugged:
Generally, it's the high voltage main capacitor - usually the largest, highest rated one on the board. Depending on the power supply, there can be more than one, but the risk is the ones that store a lot of energy. Waiting several minutes and being certain that everything's unplugged go a long way as well. Systems won't hold their charge indefinitely (though there are some exceptions that discharge very slowly) and a lot of particularly slow or dangerous ones generally have a bleeder resistor or LED built in to show you, so when in doubt, give it a few minutes and things will get safer, at least.
If you're plugged in:
Don't try to discharge anything, as it should be charged when operating. This is where careful proving comes into play, since a slip can short something sensitive or connect to something that's not safe to be probing with your current settings. If your DMM comes with those little plastic caps that cover most of the pins, they can help with minimizing the risk of touching them accidentally or shorting them to something else.
When I have the opportunity, I like using spring hooks when probing this kind of stuff - you power down, hook up the clips, then you can power up while they're connected and monitor things. Not suitable for every check and not nearly as quick, but you can make the risk really only be your equipment this way, since you don't actually have to be touching anything.
Make sure your workspace is clear, the device is properly supported (not sliding around or at a strange angle), and minimize what you touch.