Agrobacteria can deliver parts of their DNA to plant cells as T-DNA, transfer DNA. This DNA is delivered as a single strand and can be integrated into the plant genome or can be converted to a double stranded molecule by priming the T-DNA to make it a substrate for a DNA polymerase. This article describes the process, but Nature makes getting to the article hard, sorry.
What I'm interested in is delivery of DNA to mammalian cells. I tried to find articles that used single stranded DNA in mammalian cells, but couldn't find much. Maybe I didn't spend enough time searching. I saw some suggestions that single stranded DNA could trigger apoptosis, or that single stranded DNA could be used to manipulate DNA repair mechanisms to cause integration into the genome.
However, is there any way to deliver a single stranded DNA, and have it converted to a double stranded plasmid in situ? Would probably need an RNA or DNA primer, but I don't see why you couldn't pre-bind the primer and deliver the whole complex.