It is an issue with the driver for the Wifi card for the Dell Insperion series. I had the same issue with my dell, tried everything, but still kept on loosing connection or the speed would drop to 1 MBps. Was very frustrating.
So try uninstalling and reinstalling the Wifi drivers. Dell uses 2-3 kinds of Wifi chips, so make sure you download and install the right drivers.
2) In the Wifi Adapter settings, make sure you are configured for the 2.4 GHz only, sometimes the dual 2.4/5.0 will make your adapter go nuts.
3) On the router also, make sure that it is just one of the frequencies that the router operates on. Only latest AC routers are capable of really running both the 2.4 &5.0 spectrum's at the same time without any issues. If you have a smart phone download the app "Network MM" and see what the strength if the network is at different points in your house.Move the antennas of the router in different directions to see if that makes any difference.
4) If all else fails, the Aukey Brand has this small USB dongle for the AC Router specs, It is awesome and you dont even realize that it is there.
I had to use the Aukey, as all else had failed, and my connection is rock solid now, plus where I used to get 8-10MBps actual thruput(even if it showed 150MBps) now I really get 30-40 MBPS actual thruput.
Try all these and let us know .
K