Dell has a stock 460w psu for this model which has 6 pin PCIe connectors 

Dell Precision 3630 Mini Tower 460W Desktop Power Supply D460EGM-00.

it is a generic Dell oem ATX psu also used in XPS etc. desktop pc.

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The card actually has an 8-pin connector, is there an adapter for that?

I recall correctly, the motherboard use standard ATX 24 pin.  You can install an ATX power supply of your choice, most come with 8-pin. cables.

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The Dell 460w psu 6 pin has all three 12V wired. Use a straight 6 to 8 pin adapter will give you 8 pin.   https://www.dell.com/community/XPS-Desktops/Dell-PSU-PCIe-6-pin-to-8-pin-Converter-Cable/td-p/8120790

agree w chino. The Dell 460 w psu follows industry ATX standard. You may also use non oem ATX psu 450-500w that often provides 6+2 pin or 8 pin PCIe.

@redxps630​

I know this is an older thread... But if on the 460W psu, having all 3x rails on it (??) mean that it could power a 200w gpu with an 8 pin connector (6 pin plus 2 pin) with a i7 9700k? 

A 460w is exactly what you need to power i7-9700k + a 200w TDP gpu (such as RTX 4070) based on basic online psu calculator.

Load Wattage:407 W
Recommended PSU Wattage:457 W

for exmaple to feed RTX 4070., you just need to convert the two 6 pin PCIe connector to two 8 pin and then use a dual 8 pin to 12 pin adapter

@redxps630​ thankfully I believe most 4070 I'm looking at have just a single 8 pin, including the msi venus 2x