Why the usb cable keeping on connecting and disconnecting even without

The cable itself may be defective or damaged. Try using a different USB cable to see if the issue persists. If the problem goes away, it indicates that the original cable was the cause. In that case, replacing the cable should resolve the problem. Ensure that the USB cable is securely connected to both the device and the computer or power source. Sometimes, a loose connection can cause intermittent connectivity issues. Try disconnecting and reconnecting the cable, making sure it fits snugly into the ports. The USB port on either the device or the computer may be faulty or dirty, causing the intermittent connection. Try connecting the USB cable to a different USB port and see if the problem persists. If it does, you can try cleaning the USB port using compressed air or a soft brush.

It sounds like the general consensus here is that you're going to need to replace the charging port. The good news is that it's a pretty simple procedure for your phone, and the fact that the charging port is mounted on a separate board makes it inexpensive and easy. Here's a video showing you the steps needed to do the job on your phone.

Samsung Galaxy A12 Charging Port Replacement

You can find the replacement board on most of the big websites like Amazon, eBay and AliExpress; pick whichever one works for you or do a general internet search for one local to your country. Here's an example that came up on a cursory search I did.

Amazon.com: fonefunshop for Samsung Galaxy A12 SM-A125F Replacement USB Charging Port Flex Connector : Cell Phones & Accessories

Good luck; let us know what you find and how it all turns out!

Yes but my pc seems to have slowed after i plugged the usb in