The problem may well be nothing to do with hardware at all, but purely due to an recent Windows 10 update!
I've just solved the same issue by an internet search for 'very slow broadband windows 10' and came up with this solution:
1. Close the Peer to Peer Update Process on Your PC to Fix Slow Internet after Windows 10 Update
Shut down the peer to peer update process on your PC. That is to say, you need to close the channel which you can download applications and system updates from other PC’s connected to the server since it limits your internet bandwidth seeding to other users.
Step 1. Click Start menu and then type Settings to open it.
Step 2. Select “Update and Security“.
Step 3. Click the “Advanced Options” tab.
Step 4. Click the option “Choose How Updates are Delivered".
Step 5. Turn off the On button.
2. Adjust the Internet Bandwidth Settings
Since windows 10, by default, reserves 20% of the internet bandwidth for the system applications and its operating system, you can’t browse or surf on the internet with 100% internet connection. This solution speeds up the dropping internet speed by trimming down the bandwidth which is reserved for Windows 10 and system applications. Follow the step-by-step guide to tackle slow internet after Windows 10 Update.
Step 1. Press Windows shortcut keys Win + R to open Run dialog box.
Step 2. Type gpedit.msc and then hit OK.
Step 3. Give permissions. A pop-up window will open with title of Group Policy.
Step 4. Click on Computer Configuration on the right side of the window.
Step 5. Navigate to: Administrative Templates -> Network – > Qos Packet Scheduler – > Limit reservable bandwidth.
Step 6. Click on Enable.
Step 7. Change the Value from 20 to 0.
Step 8. Apply and then click OK.
3. Disable Window Auto-Tuning
Window Auto-Tuning which is enabled by default improves performance for programs by receiving TCP data over a network. Slower internet speed after Windows 10 Update could hit your computer when Window Auto-Tuning feature is “ON”. While luckily, you can disable Windows Auto-Tuning level to improve the internet speed for the Windows 10 update. Use administrator privileges to process the following steps.
Step 1. Press Win + X and then select Command Prompt (Admin).
Step 2. Type the command netsh interface tcp show global in the window.
Step 3. Check for Receive Window Auto-Tuning Level and if it is normal, you will need to disable it.
Step 4. Type the command netsh int tcp set global autotuninglevel=disabled to disable it.
You can perform an internet speed test to see whether those adjustments improve your internet speed or not. If not, you can re-enable the Window Auto-Tuning level by typing the command netsh int tcp set global autotuninglevel=normal in the Command Prompt (Admin).
As this advice worked perfectly for me, I hope you find this helpful.
