Originally Posted by MoFinWiley
What Arnyk said except that the 12v rail is the primary in all PC or server supplies. The amperages for the voltages other than +12 are all roughly the same for all wattage supplies. It's the 12v rail that scales up on larger supplies (for overclocking cpus and large GPUs). Look for ones with a single 12v rail as well.
plus...Dont tie typical PC power supplies together. The one with slighty higher voltage will try to drive the other negavtive IIRC...they will either shut-off if they have a protection circuit or meltdown.
If you can find a "good" redundant server power supply then you might be in luck. Most redundant supplies (the ones with passive backplanes) are diode isolated, so tying them together isnt much of an issue if you get more than one.
I am now running an old CV car amp (300w x2 @4ohm) off of a server power supply. My server supply puts out 70A of 12v and runs the amp fairly well.
Here's the current ratings of a 600 watt PC power supply:
+3.3V@36A, +5V@30A, +12V1@18A, +12V2@18A, +12V3@18A, +12V4@18A, -12V@0.5A, +5VSB@3.0A
Repeating what I posted above for the 350 watt PS:
3.3V@28A, +5V@35A, +12V@15A, -5V@0.5A, -12V@0.8A, +5VSB@2.5A
You appear to be right - the major upgrade to the 600 watt PS is the additional 12 volt supplies. No corresponding increase in the 3.3 or 5 volt supplies.
Counter intuitive, but true.
I also agree with your comments about the slings and arrows of trying to parallel regulated power supplies. Not a good idea, to say the least!
One possible but certain saving grace may be that with many PC supplies, the 12 volt suppl(ies) may not not regulated at all. In fact if you pull more current from the 5 volt supply on many PCs, the 12 volt supply would often increase its voltage! Or not.
Like so many things in life, don't count on this unless you test it and know for sure that it is true.
Hooking high performance audio amps to overcurrent protected power supplies is not a good idea. We are kinda being forced into going there with all the other attractions of switchmode power. We've been there for years with aftermarket audio power amps that typically had switchmode DC-DC up converters.
Take their lead - they generally have a good sized storage cap on the PS output to handle short momentary demands for lots of power.