Did you get your 9260 from a reputable source?  Some people started selling them on eBay and on Amazon as third-party sellers even before any OEMs were using them, so it's not clear how those sellers got their inventory.  If you know anything about manufacturing practices in China, your seller could have gotten units that fit any of these descriptions:

- "Scrappers", which are units that failed some part of the QA check but that the manufacturer decided to sell through some other channel.
- "Midnight runs", which are units built during unauthorized production runs at the factory so that the manufacturer can sell them at a larger profit by cutting out the company that actually placed the order.  These are sometimes identical to the true production run units, but sometimes the manufacturer substitutes cheaper components to make a larger profit on these.
- Full-on counterfeit units that may have come from a manufacturer that isn't even supposed to be making that product.

Hi Eziooo,

Thanks for posting.  Apologies that your system is not performing as expected.

Here is information from the Dell Knowledge base and a short video you may find helpful:

Connecting and Troubleshoot Internet Connectivity Issues on Your Dell Computer

Network Connection Problems

So, you use the small dash marks to denote your 5.0 and 2.4 GHz networks?  I ask because in my experience, the 2.4 GHz networks usually have a stronger signal than 5.0 GHz.

You have set up your security for the network?

Did you uninstall all of the Killer Wireless 1535 drivers and software on that system.  I had that same killer wireless on my system and liked it but changed to a 9260 for testing.  I have to decide if I want to get a new 802.11ax router next month.  I only have the one system which can take advantage of the 160 MHz bandwidth but testing is always fun.

If it helps, my device shows the Intel 20.50.0.4 driver.

Hello.

No, I did not get the card from a reputable source, I bought it from China but with ubuntu everything works perfect.

Hello, yes the small dash marks differ the 2.4 and the 5 Ghz signals.

It is all set up, old drivers are uninstalled, windows is fresh and I have le latest drivers.

Mystery!

2.4 and 5 GHz use the same antennas. The fact that both frequencies can be picked up reasonably well using the same antenna length is a big reason why 5 GHz was selected as the new standard. But a loose antenna connection might explain that difference.

Since you seem to have very good signal strength the only other thing is it can't negotiate something with the connection.  Security would be a possibility but you say that is OK.

If you had problems with the Killer card also, it may not be the card but something with your network.  If you have a wireless router you might check for firmware upgrades, if you have some type of wireless gateway from the ISP, you might check with them.

I still don't understand why your 2.4 GHZ signal is weaker then the 5.0.  You did place the antenna leads on the correct connectors? 

I have exact the same problem with my xps15 9560. Downstairs in my home I have an TP-link archer c3150, no problems when I connect with 5ghz. Upstairs I have an Ubiquiti ac-pro. When I try to connect 5ghz at the Ubiquity the same happens. Can't connect, and starts acting strange.

Other devices can connect with no problems with the Ubiquity. So it has to be my xps15. Tried everything, nothing worked.