The psu in my system is a barebones dell proprietary one sadly
But not even a single molex connector would be just weird. I also have a Dell desktop with a typical, minimally-sufficient PSU (in my case, 300W) and while it has no 6- or 8-pin power connectors for a video card, it certainly has at least one (4-pin) molex connector...
And since you said power from the pci port won't be enough, does that mean that these cards require more than 75watts? My psu might not be able to handle that!
I didn't say the PCIE port
wasn't enough (necessarily), I said it
might not be enough to provide full USB 3.0 power under all circumstances. Even x1 bus power is sufficient to drive the card itself along with a few low- or lower-powered USB devices.
USB connections provide not just a data connection, but power for connected devices as well. The maximum power a basic USB 2.0
connection* can supply is only 0.5A though, whereas for USB 3.0, it's almost twice that at 0.9A. But the connected devices draw only as much power as they need, and most devices don't draw very much power. And of course independently-powered USB devices (like things with separate, "wall wart" power adapters) draw
very little power over the USB connection at all.
If you use the USB 3.0 card only with low(er)-powered devices, you won't need the additional power connection as long as the card was designed to work (at all) without the additional power connection. And I said before, some cards are designed that way, others aren't. (Manufacturers don't seem to state that in their specs, so check the reviews or a seller's "question and answer" section to figure out whether a particular card
must have the separate power to function at all.)
I heard those aren't exactly the most trustworthy of adapters.
Where did you hear that? As long as they're not the absolutely cheapest, crappiest generic ones you can find, they generally work just fine.
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* I say "basic power spec" because there are different, higher power specs for higher-power "battery charging" ports, but those aren't the norm and I'm really not very familiar with the concept, or their technical specifications.