First of all, that 400mbps is shared, meaning two devices, if the download was the same, would split that 400 into 200 for both devices for a total of 400. Second, wireless is not perfect, the further you get and the more things blocking direct line of sight, the slower your speed gets. Also, not all wireless adapters are equal, some may give you the full 400, while others can give you drastically less. Since you have wifi, you already have a router. The tech already tested that the router was giving you the full 400. If you are simply doing a speed test, get your laptop as close to your wireless router as possible and see if you don't get a higher download speed.