....and maybe not the appropriate place for me to place this info....but from the last coop, I bought two 12V kits because I wasn't sure what I'd actually need for powering my lights this year. As a result of finally getting to task on understanding what I need, I'm 90% confident I'm going down the ATX power supply route and won't be needing my 12v kits. I'm going to keep them on hand anyways, but if someone really needs a kit I can spare one
That said maybe appropriate - nut not 100% in line with the OP but, with my two active hubs I'm still thinking I'm going to get a 850W supply that has at least a 60A rating four the 12V output. The plan for this year will likely be 12smart string megatree and one 8 dumb string animated singing tree. That should leave me a number of ports free in case of any blown fuses this season....of which i'm hoping won't happen because I've done my job keeping water/snow out of the way of the electricity ;-)
OH - and it took me a while to figure out what the heck you meant by different branch of the single supply vs a different branch. First I learn about watts, then volts, then amps, and then rails and now branches. Do you guys (gals) learn this stuff from A+ certification?