XPS 8700 new power supply 460w mismatch 6 pin ATX MB power supply

I would not test the power supply by connecting the 24 pin connector to the motherboard, because in order to turn the power supply on you need to press the power on switch. I would test the power supply separately using the following method described here (connecting pins 15 and 16): https://www.wikihow.com/Check-a-Power-Supply

Thanks Vic

Okay what I did is I read the how to I disconnected everything follow those instructions made the jumper pin stuck it in there and then connected the power cord and then at that point the green power light on the PSU was lit and it doesn't have a on off toggle switch it has a press override switch when I press the switch hoping for fan run in the case no fan however without the 24 pin connector connected to the motherboard the fans would not get any signal so I believe those instructions are not correct in the how to however before I follow your instructions I happy 24 pin connector connected to the motherboard and when I powered up and press the override toggle on the PSU the case fan would come onhowever I don't recall seeing the green light on? And I think I would have to engage the power button? I'm not sure if that green light for the PSU stays on once the plug is energized or is it requires the power switch to be engaged on the computer tower. I'll check that right now

I have connected the 24 pin an energized the plug there is no power light on the PSU and the model number of the PSU is

d460am-02

Start off disconnect everything re-energize the PSU no light press the override toggle light comes on PSU fan turns release toggle button light goes off fan stops test 24 pin for currants green pin and adjacent contacst shows 4.78 volts no other indicators of power on the 24 pin other than 4.78 utilizing the green pin and 13 14 15 each showing 4.78 and#7+4 showing 4.79

I am going to check the voltages on the 24 pin

I have cut the 6-pin off and mated the correct Commons and 12 volt / Brown - 2 wires with wire nuts and I'm ready to power, up one further question for anyone that can assist me before I fry the motherboard?

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I stopped reading there. What on earth are you doing ... cutting off connectors ?!  

Apart from that, you test PC Power-Supplies with a Digital PC Power-Supply Tester ... maybe with a multi-meter (if you know how to use it properly and know what you are doing). I still prefer the tester for obvious reasons (reads all voltages concurrently, measurement of PG, etc). 

You should not connect any of the power supply connectors to the motherboard or other devices. You are checking the PSU separately and measuring the voltages. You mentioned that you were not getting 12V at the 6-pin connector. With the jumper installed, you should be able to measure all the voltages, 5v, 12v, -12v, etc. The jumper is a substitute for the signal from the motherboard for turning the PSU on.

 I tried to match the PSU for replacement and after ordering 2 and having to send the last one back I am resorting to your assistance and myself help trying to make what appears to be a match an output but not in connectors

What am I doing cutting off connectors? The picture displays a XPS 8700 with a 4 pin ATX power supply connection the new PSU has a ATX 6 pin + 2 connection the answer is this picture.

Of the six wires 2 are capped off the remaining four provide 2 Commons black + 2 12 volt Brown

So, apart from the scary cutting ... the other thing that comes to mind is you have no way to know how the 12v rails are distributed (as you don't have the internal schematic).

The Alienware 850w PS should have worked fine, provided you have the proper (proprietorially matched) modular cables.

Would be easier to drop-in a conventional Corsair or Seasonic PC-PS (SMPS).

https://www.dell.com/community/Vostro-Desktops/Vostro-460-XPS-8300-Upgrade-Adventures/m-p/6055730/highlight/true#M1225

Off-the-shelf brand new PSU I am not considering that's bad just for procedural effect.

What's throwing me off is I wasn't getting any readings off the 24 pin connections but if I hold the power override toggle switch down the green light comes on and then I do get the correct voltages out of the pins. Now I'm not sure why I have to hold that power button down to energize it? Even with nothing connected an energizing the PSU the whole light doesn't show until I press the button?I I want to try and override the power button by shorting it together to see if it's the power switch is faulty I did pretty much butcher that switch when I reassembled the case. I hit started on this over a month ago and got busy so that's some just coming back to it and I forget some stuff but I've got the file for that power switch somewhere see if I can find it.

Pinouts and the voltages on the pin for each PSU connector are listed here: https://www.lifewire.com/atx-power-supply-pinout-tables-2624590

Click on the link for each connector to see the table. While I agree with @Tesla1856 , not everybody has a power supply tester readily available so at least with a voltmeter you can test for the proper voltages at each connector, especially if you are going to be cutting off connectors and putting different ones on.

https://www.newegg.com/p/1A0-002Y-011Z7?item=9SIA4A05RX7356

Seeif this link works to show you I was trying to replace the Dell power supply with another one and this is at the Newegg site if it opens up to the correct site look at it it shows 1 through 6 displays if you go to the number 6 display you see that it shows the correct wiring that I needed and that is what I ordered but what I got was just two accessory wires that were 6 pin plus 2 ATX

Not an 850 watt it was sold as a 460 Watt Alienware replacement.I did that as a potluck to see if I could make it work since I was having trouble finding anything with all the same accessory cabaling

This is the one I'm trying to make work