You apparently have the mini-tower version of this Dell series, who power supply has no 6-pin PCIExpress power cable. Oddly, the smaller
slim-tower model odes have one, but that won't help your situation. There are two solutions:
(a) find an ATX power supply that does have the connector you need. Measure the dimensions of your current and very cheap $20-USD Bestec power supply and find a better ATX power supply that will fit in the space. BesTec is one of the cheapest OEM brands around (that's the way it goes with Dell PC's). There are other budget ATX supplies that are cleaner, better equipped, and not very expensive.
Or
(b) I can't see that well from your photos, but if you have a free 4pin molex power cable available inside, try a 4-pin to 6-pin PCiExpress adapter. They are dirt cheap:
https://www.amazon.co.uk/4-Pin-Molex...xpress+adapter.
I see only one hard drive. I'd try to find a 2nd hard drive for that PC. Capturing operations to the same hard drive that is home to your operating system can cause trouble, such as dropped frames or audio sync problems.
For power rating, I'd say 300 watts (if the BesTec actually outputs that figure) is barely enough for capture with that card. It would be better if you could find another mere 50 or 100 watts.
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