USB3 PCIe card without extra power plug

I bought several of these cards, trying to find one that works with older
Centos linux. Most have a PATA Molex plug to import extra power. One has a
floppy disk power plug instead! And one has no extra power.
Now I believe PCIe x1 is good for 10 Watts. The powerless card only has 2
USB sockets, but if both were sucking in 900 mA, you would be cutting it
fine. So would you only use 1 drive on such a card?
Well, anyway the cheaper adapter cards slow down when you plug more than
one device into them. The "superspeed" cards with PCIe x4 would be ideal,
but they are more expensive to buy at random, hoping they will work.....