I'm running the dynamic hashvoodoo release capped at 200 on mpbm and a laptop and i've been noticing my rig doesn't like more than 17 boards connected at once. It always drops 2 random boards a few hours after I reset them. Each time one of them drops I swap out the usb cable for a new one. It's possible they aren't getting enough power, but I have them connected to a 1000 watt power supply on a 1500va/1000 watt UPS that hasn't given any warnings, and the rig only draws 950 from the wall, so i should have ~250 watts to spare. I'm going to split the rig up and see what happens over the weekend.
You have to be a little careful on what an individual ATX PSU will do. The additive of individual rails is often more than the overall rating but conversely that doesn't mean you can get the entire 1000 watts out of the 12V rails.
In some power supplies the 12V is also split and individual sections have a limit and it is possible to exceed the limit on one section whilst under capacity either overall or even in other sections.
There is another aspect which probably isn't a big factor in modern ATX supplies but I will mention to be complete and that is where the 5V or 3.3V is underloaded and causes an issue. In older supplies there was often a primary regulation based on usually 5V loading. Low or no load on the 5V typically lowered what I will call the excitation of the power supply and basically it drops too low to provide enough energy to 12V circuits. Some of you may have noticed that we put a small loading on our PDB for 5V and 3.3V to avoid this issue.
upon further inspection i indeed was drawing too much from the power supply. switched out to a more efficient 1200 watt and everything is humming along nicely and drawing less power too! Now to find something to do with this newfound free time.