Is it possible to add WIFI by adding a USB wifi dongle in devices that wifi doesn't work?

With ASUS RT-N18U for example, wifi doesn't work. Could I make it work with a USB dongle? Or it doesn't work like that?
I have plenty of USB wifi's, and one Tenda U12 usb dongle, which is USB 3.0. Much faster. I don't need too much speed.
Edit: I tried Tenda U12 on both USB2 and USB3 ports. It made router act weird. I had to reboot. I assume not enough power for that.

Yes you can do that, as long as the dongle has a supported chipset of course. As you said, do not expect much performance, but it is a good way to run a few nearby IoTs or access the router for configuration etc.


Can I perhaps change the WIFI chipset inside the motherboard? I have the electronics equipment also. But what chipset to apply to it instead.. It must be complicated.

You can buy a device that's actually supported, there are often quite nice things on the used markets.

Did you even look inside?
If you can do it on that device, well, colour me impressed (not that it would make any sense at all).

I've bought an Allnet ALL-WA1200AC USB dongle (chipset is supported by the kernel) and it works with a TP-Link C2600.

As @mk24 said: look for a supported chipset. Allthough a supported device can fail, if the USB port of the router doesn't deliver enough power. Some devices use more than 500 mA.

I can't find a netgear here, I actually have a netgear r7500, but it's faulty, it can't get power, I need to repair it. It's a very good router.