Recently, I have not been inside a PSU that did not have a bleeder resistor on the HV caps. Perhaps the industry has gotten wiser. Still, it takes around 10 seconds or so for the level to drop below hazardous once power is removed. Never assume your unit has one. Also, many current PSUs insulate the switching transistor collectors from the heatsink, but many less expensive PSUs don't. That means those big, exposed aluminum heatsinks may have hazardous voltage on them. The hazardous voltage is not necessarily restricted to just down on the circuit card. Don't forget the AC jack. If you are "live" testing keep your fingers, tools, and loose assemblies away from that AC jack. In 23 years servicing switching supplies and longer on linear supplies, I have lost count of the number of times I have been "bit" by them and obviously survived. We're not talking overhead power line or lightning strike levels here. That, having been said, don't work on one when you are in a hurry, distracted, angry, in an altered state of consciousness, or sweating like a pig. Think before you act and leave yourself an out. Most of the injuries I have received came from jerking my hand and encountering a sharp object adjacent to it, most often sharp sheet metal.
Just like a power tool, firearm, automobile, etc., respect the potential to cause harm and you'll be okay.
Hoot