Why won't exact replacement PSU work but generic will?

Hi kennyneon,

I appreciate the time and effort that you took to troubleshoot the issue. I understand that the higher wattage PSU works fine on the system. Please let us know if you have recently added any new hardware on the system.

546 Desktop system are shipped with normal 300 watt PSU. Please let us know what were the PSU that you tried on the system.

Also, when you disconnected all the parts in the system do you hear the beep codes coming from the system. If you have a similar motherboard available you should check in the system to isolate the issue.

Keep us posted with the results so we can advise you further.

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Thank you Sandeep for your fast reply. I will have to check specs later when back at the office. The substitute PSU that works came from a Latitude Desktop. It may be 400W but I will check. There has been no new hardware and as far as I know all hardware works. When I disconnected parts there were no beep codes - not even the fan moving. Unfortunately I do not have another similar motherboard to check.

I would just use the substitute but it does not fit.

You can also do a crude PSU test:

Power off and unplug.  Press/hold power button for ~15 sec. Unplug the connector from the PSU at the motherboard.  Use a bent paperclip or short wire to jumper the GREEN wire to a BLACK wire in that connector. Plug the unit in and see if the power supply turns on (fan runs) and hard drive spins up.  (NOTE: Do not cut or remove any wires from that connector.)

This doesn't prove it's a working power supply, but if it won't turn on with the jumper then the power supply is defective.  Unfortunately the only way to be sure is to replace it with a known good supply, which you've essentially done with the one that doesn't fit the case. 

I did the tests on the original Hipro and  the replacement Hipro and the fan turned but if connected to the motherboard fans do not. These models are 300W. The ill fitting replacement is also a Hipro. Curiously it is rated 305 Watts! Could the 5W difference be cause for the system not working? It seems the simple answer will be to find a proper fitting higher wattage PSU. The question I still have is if the PSU is not putting out due to this 5W difference where is the event happening. Is the PSU sensing an overload and shutting down or is the motherboard sensing the overload and in turn telling the PSU to shut down? Thanks in advance for your help. 

Hi kennyneon,

It seems to be the issue with the motherboard rather than the power supply. As 300 and 305 watts is not much of a difference and it should work fine on the system.

It could be an issue with the ATX connector on the motherboard of the system which is not letting power supply to start completely. You could either get a replacement motherboard for the system or take it to local repair shop to test and confirm the faulty part on the system.

If the system is under warranty then please contact me through a private message by clicking on my name highlighted in blue. On the next page, click the envelope icon and provide your service tag and contact information so I may access your system records.

And, if the system is out of warranty then you contact our Expired Warranty Support at the link below:

http://dell.to/12LmNBq

If you have any further queries please feel free to contact us.

Thanks, I'll look into the motherboard connection though I'm not sure why two of the same model do not work and my substitute model does. It's out of warranty so I'll check.

Thanks Sandeep. The one question that keeps bugging me is if the issue is for example the atx connection on the motherboard why is the 305W PSU working fine and the older and its twin PSU not working.

Hi kennyneon,

Please check the same at your convenience and let us know the results so we can advise you further if required. If you have any further queries, please feel free to contact us. 

Hi kennyneon,

I understand you tested two different PSUs on the system and they caused the same issue on the system. Only PSU that worked was with a higher wattage than 305 watt.

Motherboard sends auxiliary power to the PSU to initiate it for the startup. If PSU doesn't start then it comes to two things either PSU is not right or motherboard is not sending the signal.

Your issue seems to be intermittent as it worked with one of the Power Supply. So I believe it would be best to take it to local repair shop and check all the PSU with a different motherboard to confirm the cause of failure.

Hope it helps. If you have any further queries, please feel free to contact us. 

Thank you. That is the information I was seeking.

Hi KENNYNEON,

Its great to hear that your query has been answered to your satisfaction. If you have any queries in future feel free to contacts us.