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I am trying to modify a Delta DPS-400AB-17 server 1U power supply to support a desktop motherboard and graphics card. The power supply has an 8 pin 12V EPS connector attached to a 21A 12V (252W) rail. My plan is to turn this into a 4 Pin ATX connector + a 6 pin PCIe connector (my motherboard only has a 4 pin CPU plug).

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This theoretically shouldn't be a problem as I am not splitting up any wires, each receptacle is getting its own wire from the power supply (except the sense wire - which my understanding is doesn't actually complete a circuit). However, this would mean the rail that this is connected to could be at 70-80% utilization, meanwhile the other rail (which only has a 24 pin motherboard and some unused SATA connectors) could be at only 10%. Is having this kind of differential between the rails a bad thing?

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  • \$\begingroup\$ There's a good chance all of these wires are wired in parallel anyway. Are you sure they are separate rails? \$\endgroup\$
    – user253751
    Aug 12, 2020 at 19:47
  • \$\begingroup\$ @user253751 I'm not totally sure, but 99% of the time on these server power supplies, everything except the EPS 12v connector is on rail #2, while the EPS 12v is on rail #1. That would mean both the CPU and GPU are both on rail #1, and nothing that draws a significant amount of power would be on rail #2 \$\endgroup\$
    – Palin567
    Aug 12, 2020 at 19:49

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This is a non-redundant 400W supply with primary load = 12V and other smaller load voltages. The Delta supplies > 1KW appear to be redundant with dual 12V outlets.

i.e. All wires are common for V+,0V.

Generally, PC PSU's regulate off 5V and use tight magnetic coupling with winding ratios to generate the other voltages. But in Zeus servers the main load is 12V so there is no worry loading the unused +5V.

enter image description here ref

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  • \$\begingroup\$ I see that the Delta website does have 32.5A listed as the +12V, but when I look at the actual label on the PSU it shows 2 separate +12V rails each rated for 21A. It is bad if one of those rails is being utilized significantly more than the other? \$\endgroup\$
    – Palin567
    Aug 12, 2020 at 20:29
  • \$\begingroup\$ I doubt it....... \$\endgroup\$
    – Tony Stewart EE75
    Aug 12, 2020 at 23:21
  • \$\begingroup\$ We don’t know what we don’t know but there’s nothing fundamental in PC power supply design that suggests it’s not ok to load one output at 100% rated current and another one at zero. \$\endgroup\$
    – Frog
    Apr 17 at 21:36
  • \$\begingroup\$ If you open the power supply up you will find all the +12V on a single bus, same for +5 and ground. This being true the power supply does not nor does it care where the load is, it will simply do its job and supply power. \$\endgroup\$
    – Gil
    Apr 17 at 22:09
  • \$\begingroup\$ @Gil if there is a common core to a forward converter, the main +5V in PC PSU's is the only one with NFB. So reducing 12V load will only raise it's voltage slightly. Cross-regulation specs apply. \$\endgroup\$
    – Tony Stewart EE75
    Apr 18 at 13:57

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