FTDI Chip to Serial port
Beware that there are several versions of USB / SERIAL adapters. The standard type, and the kind you want for connection to your server's D-Sub 9 connector, will be one that comes already with its own D-Sub 9 connector. These have an internal FTDI chip that converts from USB to a serial logic level signal and then an RS232 transceiver part that converts the logic level serial over to the +/- bipolar signalling used by the standard serial port. 



You will most likely need a null modem adapter between the USB/SERIAL adapter and the server computer serial port connector. A really convenient type of null modem adapter for this use looks like this:



The other type of FTDI USB to serial adapter is one that does not include the RS232 transceiver chip. These bring out the logic level serial lines so that they can be connected directly to a microcontroller or other circuit. It alleviates the need to put standard RS232 transceivers for a debug port or programming port on MCU hardware to save space and cost whilst at the same time when the usage model is for very short cabling lengths. One example of this type of FTDI adapter looks like this:

 

Note that is not possible to try to use a logic level serial adapter to "talk" to the standard RS232 port off your server. The voltage levels do not match and the logic level signals are logically inverted from standard RS232 signals. (i.e. the RS232 transceiver parts have a logical inversion through the part).