For yeast and other organisms, DNA can be readily taken up into the cell naturally or through membrane disruption. What does applying a voltage to cells do exactly that allows more recombination to occur?
Electroporation is a fairly common way to introduce exogenous nucleic acids into cells. Its name essentially describes the process - an electric voltage potential is applied across a biological membrane, eventually leading to the production of conducting hydrophilic pores. The image below is from the Wikipedia page linked above, showing non-conducting (upper) hydrophobic and conducting (lower) hydrophilic pores. Depending on the voltage, membrane composition, and other factors, these pores can eventually "heal" and close back up, or join together and lead to the rupture of the cell.
Electroporation is used in the lab as a method of transfecting or transporting nucleic acids (usually DNA) into cells, to make them express genes they otherwise wouldn't, or to otherwise alter the genetic machinery. The transfected DNA can either remain in its own structure (such as a plasmid), or be incorporated (recombined) into the host genome, similar to what happens during a retrovirus infection. Whether or not this happens is dependent on the structure and sequence of the construct being introduced, not the method of introduction.
So, in reference to your question, electroporation doesn't do anything that directly allows more recombination to occur - all it is is a method of transportation. However, electroporation may allow for certain constructs to be introduced into the host more efficiently, or for a larger quantity of them to be introduced, leading to a greater transformation efficiency. Some cells, especially primary cells like neurons, for example, may only be transfected with any sort of efficiency with electroporation. However, electroporation can also have its down sides, as it can be rather stressful to the cells, and if the voltages and timing aren't properly adjusted can lead to high levels of cell death.