Recently I've changed jobs, and consequently the field of research has also changed. But I'm still getting proposals for publications in the previous field, and it is interesting for me to accept some of them. My concern is about which affiliation to use: on one hand I gain all the knowledge in that field while working on the previous employer, also I hope they can cover my expenses related to the publication. On the other hand, I do not work for them anymore, and my current company has very little interest in my old field of research, and probably will not support it financially, but I think it is wise to mention them as well. As a compromise I'm thinking to put the previous employer in the affiliation, and the name of my new employer in the footnote, something like "currently at XYZ". Surely I'll discuss this issue with both, although the opinion of the community is also very valuable.
If you have written the publication only with the resources and support of the former employer, then it is perfectly acceptable to do what you have written, and list the old address as your address for the "active" affiliations, and include a "present address" affiliation to show your updated physical location.
However, if your new employer does provide financial support, then you should list them accordingly. This is especially important if any of the actual research that makes its way into a publication has been performed while working for the new employer using their resources.
I would list the current affiliation in the address field (that field just tells where people can find you, not much more than that) and start the paper with an elaborate paragraph starting with "This work was made possible through the generous support by.... ". This way you kill both birds at once.