Very strange wifi speed issue

Hello,

I have no idea of what's happening with my wiFi connection, so any ideas will be very appreciated.

I'm using a tp-link TL-WN725N adapter on a windows 10 PC, and I currently have a 150Mbps internet link.

The problem goes as follows:

Using 2g wifi (the only one supported by my adapter), I can reach ~50Mbps (speedtest.net) on any connected device (samsung galaxy s7, macbook, asus eeePc), however, on this PC using this adapter, the maximum speed is only ~1Mbps. I first thought it was an adapter problem, however this is when things get strange: using my samsung s7 connected to 2g wifi network, I can route the connection, and then, connecting the adapter to my cellphone, I can reach the same ~50Mbps on my PC. Very weird.

2.4g wifi -> PC = ~1Mbps
2.4g wifi -> galaxy S7 -> PC = ~50Mbps

Any thoughts on that?

Thanks!