USB K/M to PS/2 Converter - USB keyboard & mouse to control native PS/2
The Adder KMU2P converter adapts USB keyboard and mouse connections to traditional PS/2-style inputs for use with older PC systems and equipment. Adder's KMU2P converter emulates the presence of a keyboard and mouse (via the PS/2 connectors) to the device at all times. This means that when used with a KVM switch, there will be no delay in response when switching to this channel.
Answer: Thank you for your inquiry,
Yes sir, you can use the Adder KMU2P without the second USB port plugged in.