Hello alakhgulati.
I know that some PLC's have USB device ports, and they can be used to program via a USB host port on the programming PC.
Examples that I know are Modicon M340 and Mitsubishi Q series.
Completely different are the embedded PCs, working as PLCs, that have USB host ports onboard. To these you can attach USB devices. Embedded PCs running Windows CE has a limited number of compatible USB devices. Embedded PCs running Windows XP Embedded can in principle connect to any USB device.
Examples of Embedded PCs running as PLCs with USB ports are Beckhoff CX series, and Siemens Microbox 427B RTX.