Only the "Ex" suffix is an actual manufacturer-specific suffix out of those you mentioned.
GTX 1660 means it is a GTX 1660 card
GTX 1660 Ti means it is a GTX 1660 Ti card
GTX 1660 Super means it is a GTX 1660 Super card
Differences between these are not manufacturer-specific, all are reference designs by NVIDIA. You can find the differences at NVIDIA's website, e.g.
https://www.nvidia.com/en-eu/geforce/graphics-cards/16-series/With regards to GTX 1660 Super EX (and X), you would have to go to the manufacturer's (GALAX, which is not ASUS) website to see what is the difference from the reference card.
Most of the suffixes do not carry much information (even the 'OC'/'ULTRA OC'/etc. ones), so you will need to compare the card's information with reference card's data, but some of the suffixes do:
- LP (low-profile)/MINI and similar indicate cards specifically targeting small or OEM-specific cases
- Blower indicate cars that blow hot air out the back of the case
- Twin/Dual and similar indicate cards with two fans
- Triple/Trio and similar indicate cards with three fans
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