Two types of keyboard
There are two types of keyboards - PS/2 keyboards and USB keyboards. The difference between them is in the plug that they use to connect to the computer.
PS/2 keyboards are the original keyboards. They have a round plug.
USB keyboards are the more modern keyboards. They have a rectangular plug.
Differences in Signalling
PS/2 keyboards talk to the computer using the old method, a 30kHz electrical signal.
USB keyboards talk to the computer using the modern method, an electrical signal between 1.1Mhz and 433MHz.
Although there may be different adaptor plugs present on the keyboard cable, such as a PS/2 to USB adaptor plug, the electrical signals used depend on the plug that is actually inserted into the computer motherboard. The keyboard itself senses which electrical signals are needed, and talks to the computer motherboard using the correct method.
A device designed to record from a PS/2 keyboard will not recognize USB electrical signals, and vice-versa.