I own a fairly old Dell Inspiron 620s with Intel Core i3 2100. which has 8 USB 2.0 ports. I wanted to add a PCIe card that could add 2 3.0 ports with faster data transfer speed (because we live in 2018).
I'm looking forward to buy This Product, description says it only supports Windows, Driver page only has drivers for Windows and I talked to the Company Rep and he generically said "It only supports windows". but in past I've been lucky with Wifi adaptor cards (realtek) and other cards without any mention that they supported Linux in any form.
User manual says that it has VIA VL805 chipset, but I've not found a single proof that this card is supported on Ubuntu, but other VIA cards are supported.
what should I do? any suggestions?
Yes, the VIA VL805 is compatible with the Linux Kernel, and works with Ubuntu.
Here's proof: A bug report of support being provided.
Note that compatibility and good support rely upon cooperation by the manufacturer. They make their hardware compatible with Linux.