And is Newegg a legit site? Because they have some nice prices.
Very much so. I have been purchasing parts from them since 2004.
I have never purchased parts from 3rd party vendors on Newegg, though, ONLY where the seller is listed as Newegg.
And what is the difference between gtx 1660, 1650 super, and 1660 super?
Performance, and power consumption.
From lowest to highest performance: 1650 Super, 1660, 1660 Super.
Power consumption is about 100W max for the 1650 Super, about 125-130W max for the 1660 and 1660 Super.
It does look like the Dell you have uses a nonstandard power supply form factor. Do you still have the power supply? If so, please check the label on it. According to
this thread on the Dell forums, it came with either a 290W PSU, or an optional 365W PSU. It also mentions in that thread using a standard PSU, but that such a PSU would need to be external to the case I think.
Here's what the sticker looks like for the 365W unit:
Even with a 130W video card, I'd say you're pretty safe if your Dell came with the 365W PSU.
With the 290W, I'd probably want to see what the specifications sticker on the PSU looks like, but it should still be able to manage the video cards you mention.... if and
ONLY IF it has the PCIe power connector your GPU will need. I think any of those video cards should only need a 6-pin, but I can't be certain.