The specific reasons are as follows:

The reason why PCR products run faster than plasmids is that their migration speeds in agarose gel electrophoresis are different. PCR products and plasmids are two different DNA molecules with different shapes and sizes, and PCR has smaller molecules so it passes faster.

The products of PCR are usually pure DNA fragments. These additional DNA sequences can increase the size and shape of DNA molecules, causing them to move slower in agarose gels. The DNA polymerase used in the PCR reaction causes the DNA chain to grow continuously, producing unstructured DNA molecules, which will also affect the movement speed of DNA molecules in agarose gel.