I have 3 cubes, one is acting up (all X's) but I have been doing a lot of fiddling
with power supplies and good power is absolutely required.

I have one cube running on a generic ~600 W ATX supply, with a single
PCI-E harness. At first, it went through a splitter, which lasted a couple of days until
it melted.  Then, I soldered the splitter ends directly to the ATX supply, which
now runs great, nice and cool.

Cube #2 is wired to a 1000 W HP server supply that also powers four ASICMiner Blades.
It's been working flawlessly.

Cube #3 is wired solo to a new 850W Corsair RM850.  This turned out to be the weirdest of the
bunch.  The RM850 has two independent PCI-E harnesses, which each have a pair of
PCI-E connectors daisy-chained.  But there is apparently a defect in this power supply
because the Cube won't work on one of the harnesses, even though the
power supply works under other test loads. It works 100% using the "good"
PCI-E harness, daisy-chained to both Cube PCI-E power ports, but won't work
when plugged into both harnesses.  There is no noticeable heating of the PCI-E cables
when the Cube is powered by a single harness with the Corsair, and noticeable but
modest heat using the generic ATX supply.

One of my Cubes has intermittent ASIC failures and start-up problems, but that does not
seem to be power-related.  Believe me, I've tried everything. SSB is working with me to
get that issue resolved.

All my Cubes are set for overclocking, and (once you have 100% good power) that
does not appear to be related to any problems.  I also have a supplemental
200 mm fan exhausting air out the front of each cube, just to be safe.

These are some fussy miners, but many of the problems can be tracked to
system power supply issues.  I'm glad that I happen to have had enough
different scenarios to test out in order to help diagnose and troubleshoot
what does and doesn't work.

-Mark