Investigate a 100 Mbps Wired Link Before Buying Faster Internet
The speed printed on a wireless router's box can describe its radio capability rather than its Ethernet ports. A computer reporting a 100 Mbps wired link is describing one local connection. Before changing an internet plan, establish which part of the path supports which rate.
Write down the route from the computer through any dock, wall socket, switch and router. Check the exact port specifications for those devices. A fast router can still have a particular port or attached adapter that limits the connection being used.
Compare capability with the negotiated link
Inspect the computer's reported Ethernet link speed using its normal network status controls. On managed equipment, the switch may also report the rate for that port. Record both observations with the port numbers so the same connection can be identified later.
TP-Link explains that the wired link depends on the router's LAN port, Ethernet adapter and cable. If a component supports only 100 Mbps, that reading can be normal. A wireless figure such as 300 Mbps does not upgrade the physical LAN port.
If every component in the documented path should support a higher rate, test a known-good cable and a suitable alternative port during an agreed interruption. Change one segment at a time. Keep a note of which substitution changes the negotiated rate rather than replacing several items and losing the evidence.
Measure the outcome at the right layer
After the link rate is understood, repeat the actual work transfer or an appropriate speed test. A higher negotiated rate is capacity, not a guarantee that a remote server or internet service will deliver that rate continuously.
Likewise, an internet result can be limited by the router's WAN port or provider connection even when the computer's LAN link is faster. Keep local-link observations and internet measurements in separate columns. This makes a purchase decision depend on the identified limitation, rather than on two marketing numbers that describe different parts of the network.
References: TP-Link link-speed explanation.