As I understand it, you have two tables and two drawings:
1. You have a table where records have latitude and longitude values, but no other attributes. At each such latitude/longitude there is a transformer.
2. You have a table that has a list of all transformers with a variety of fields in that table (it would help to see the schema for that table). None of the fields are latitude or longitude values. Some of the records may have a name or comment, like "school", but none of the records have fields that can be used for geocoding, such as 125 Main Strasse, Hamburg, Germany. Some of the records don't even have a comment value like "school".
In addition you have two drawings:
3. You have an abstract, non-geographic diagram that shows the connection of transformers to electrical lines. The illustration is too small to see how those transformers are labeled.
4. You have a drawing or table that shows the geographic location of electrical lines (perhaps as a series of lat / lon locations), but which does not have any information about the location of transformers on that line.
Is the above correct? If so, it seems you are stuck with a process that involves a lot of manual labor. Manifold can help reduce that labor, but it cannot eliminate it.
For example, I'd start by taking the lat / lon dots from 1 and doing a spatial join with 4 using a buffer on the lines so that now you have the line for most of the lat/lon dots, and can by inspection guess at the lines where the lat/lon dots are close to intersections where buffers of lines would overlap.
Next, you have to guess at which transformers in the list of ones with attributes are which lat/lon dot. That can't be fully automated because not all of the records with attributes have info in them that without ambiguity can join them to the lat/lon dots.
But by using the info that you have, and using sensible backgound layers like Points of Interest, schools and others from OpenStreetMap or Google or whatever, and by keeping multiple tables open so you can quickly copy/paste, you could evolve a workflow where fairly rapidly as you go down a line you'll be able to identify the relevant record in the attribute table that corresponds to a lat/lon dot. Copy/paste an ID field from the dots table and then you can do a join on that.
It's manual, but using Manifold effectively with plenty of screen real estate and a few opened table windows, it could go very fast, like a couple of records per minute. One long day and you're done.