Hello, 

for your information, the TL-PA4010Pkit has the 100Mbps ethernet ports. that is to say, the maximum speed from it won't be higher than 100Mbps.

Back to your case, we can do some troubleshooting: 

first, you can follow the below instruction to narrow down the issue and tell us some details:

https://www.tp-link.com/en/faq-2231.html

a. the speed you can get from 4010P when it is in the same with main router.

b. The wired link speed of your computer; how to get it: https://www.tp-link.com/en/faq-2265.html

c. The powerline link which shows up on the tpPLC utility.

d. The speed you can get from the main router by wired cable with the same computer.

Any updates, just let us know.

Good day.