Dual power supplies - one of them only works as secondary now

I'm sorry if this question has been asked, but my computer has not been working and it is right now. I'll go scour the forums for other info or help, but if anyone has any experience with this or can point me to another source, I'd be grateful. I did see the walkthrough for power supply issues, and it did not appear to address this, and I do not have access to a voltmeter.

In my computer I run a dual power supply setup, with a 470 watt and a 350 watt power supply ganged to each other and powering different things. Everything else is rather power intensive: DP55WG motherboard with core i3-530 processor, 6GB ram, 4 hard drives, dvd drive, creative sound card, nVidia GTS 250 video card. So I used the 470W power supply as primary, to power the board and processor and the like, and use the 350W to power most other things. It seemed to work quite well.

Recently after I shutdown the computer, after leaving it on most of the time, it wouldn't turn back on, at all. I thought the RAM was causing a problem but in any case, after putzing around, I figured out that the 470W supply no longer will function as a "primary" supply, nor at all when it is used standalone. However, it will work perfectly fine when it is connected as secondary to the 350W, where the 350 powers the board, and the 470 powers whatever else.

Since no wiring changed, and the power supply is functional otherwise, I have NO clue as to why this situation is occurring. This whole setup was accomplished using a standard dual power supply connector, not something I fangled together. When I plug it in one way it works, the other way, it won't work at all.

Either way, the standby light for the supply in question does come on on the motherboard - just nothing after that.

My goal is to have the 470 work by itself, as ultimately I planned to move that one into a single power supply system and replace the original 470 with a similar one with more connectors. At worst, I can leave it as secondary to the 350, but I don't understand why I have to. I would feel much better about the system's stability if this 470 would work on its own, as it appears that it should.

Any ideas?
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  1. It sounds like the 470w is dying to me.

    I am not an expert on dual PSU setups, but from what I understand about PSUs in general it seems plausible that the strain on the 470 has caused the performance of it to deteriorate to the point it can no longer do the same job it used to be able to do.

    In my past experience, I have seen many times where people left their computers on for months at a time between power offs and it happened that one time they turn their computer off and it can't turn back on.

    In those cases, the computers usually work again perfectly with a new PSU.

    I think I would consider getting an XFX 550w if I were you and using only that PSU without the 350 attached.

    If you can borrow a PSU from a different computer you could confirm this theory before purchasing the other PSU.

    It won't help if you can only borrow another one that isn't at least equal to the power of the two in question, though. If it is a problem of not enough juice, you wouldn't be able to test it with even less juice than you currently have.

    If there is another one you can borrow, I can advise if it would be a reasonable test PSU if you tell me the maker/model/age of it.
  2. I'd be convinced that the 470W was dying based on its usage over the years, except for the fact that the standby light does come on when it's plugged into the board, and when it's connected as a secondary, it does power up fully. When attached as a secondary, you wouldn't think anything was wrong with it - the drives it supplies power to work properly.

    This would probably be better placed in the power supplies forum, if it's possible to move it there.
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