@Chuug 

Hello, the tpPLC speed is not the actual speed, instead, it is the powerline link rate between the 2 adapters; the speed we can get from is about 30%-40% of it, combined with the interference, the actual speed even be slower. 

While cause the current speed is just 10% of it, we can do some troubleshooting on it. 

1. The speed you can get from the TL-PA9025PKIT with computer connected to it only.

2. Please click here to verify the wired negotiation speed of the computer. 

Note：The steps are the same, while you need right click on local area connection or ethernet connection. 

3. Try to move them into the same room to test the speed, or change another wall sockets to plug them.

Below is a guidance you can refer to narrow down the issue. 

https://www.tp-link.com/support/faq/2231/

Best regards.