Unfortunately, your suggested way does not work. It is not possible to connect with an USB plug.
The reason for that: serial and USB use different levels for data transmission. Also Windows needs a driver for every USB connector.
The solution for you will be this: You solder a sub D-9 connector onto the cable. The connector goes into a serial<->USB adapter. And you attach this adapter into the pc. We can deliver a SUP D 9 pole connector and also an adapter.