Hi,
Check that there is 20V DC on the output plug of the charger.
If the charger is OK, open the laptop and connect the charger and check if there is 20V DC where the [https://www.ebay.com/itm/255138961755|DC-In jack part #5C10S29899] plugs into the motherboard. (supplier example only).
Here's the [https://download.lenovo.com/consumer/mobiles_pub/c340_15_flex_15_hmm.pdf|hardware maintenance manual] for the laptop. Go to p.49 to view the procedure to remove the DC-In cable to see how to access it so that you can test.
If there is no voltage at the motherboard plug end of the DC-In cable then most likely what has happened is that the +ve centre pin in the jack has broken internally and the jack will have to be replaced as it cannot be repaired. Search online using the ''part number only'', mentioned previously, to find suppliers that suit you best.