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My old PC's ATX PSU died and I got a replacement in the form of a DELL 250W Power Supply model# HP-P2507FWP.

It has the exact set of connectors (except for an additional, unused, 6-pin connector), including the main 20-pin connector (also see this reference for standard v 1.x with 20 pin)

I plugged everything in, expecting my PC to come to life again, but while the green LED on the motherboard lights on as soon as I plug the power cord, nothing else happens when I press the ATX (momentary) power on button.

At first I thought that I ran into the infamous Dell proprietary (non-standard) ATX design, but when I compared the colors of the wires, they were all identical!

My next step is to actually measure voltages across the various pins to see whether indeed the colors match the documented voltage values but I still find it strange that I couldn't find any documentation or reference regarding the wiring of this particular PSU model.

More specifically, I have the following questions:

  1. Why do two websites that used to sell this PSU, claim it as having a 24-pin connector, not 20-pin? (one of the even has a photo of that 24-pin connector! and I can tell you with utmost certainty that mine has a 20-pin connector and the HP-P2507FWP original DELL label on it.
  2. Why is DELL's wiring's color coding identical to a standard ATX, despite the article describing even the colors being different?
  3. If my particular DELL PSU is standard... Are there additional plausible explanations for the fact that my PC won't respond to a power on signal?
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This problem description sounds very similar to yours. Could be bad capacitors? –  scatmoi Mar 24 '13 at 14:36
    
Indeed this turned out to be a problem of bad capacitors. Thank you! Please post as an answer so that I can accept. –  Eternal Learner Mar 30 '13 at 16:14

1 Answer 1

up vote 2 down vote accepted

Based on what you have described so far (including the confirmation of bad capacitors as the source of the problem and that now it works for you):

  1. I don't know, but a 24-pin connector is really a 20-pin one with the CPU 4-pin connector appended to it. Some manufacturers (e.g. Antec) actually ship their PSU with a 24-pin connector that can be converted to a 20+4 set by sliding one of each other (pretty clever if you ask me).
  2. Because you happened to stumble on a standard DELL PSU connector?
  3. Yes, bad capacitors. It's very common in those types of PSUs.
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