On a circuit with one transformer supplying power and one or more consumer transformers, the consumer transformers take a proportionate share of power to prevent the connected wire from overloading. However, if a second supplier transformer is added to the same circuit, the consumer transformers will each draw the maximum amount possible (in some cases, even multiplied by the number of suppliers), even if it overloads the wire. The expected behavior is that the consumer transformers balance the load as with one supplier transformer.
The behavior as currently implemented is inconsistent, as it breaks the concept of transformers protecting circuits (and possibly the concept that power suppliers don't count towards overload limits). Similar behavior can be seen when a charged battery is the sole supplier to the consumer transformers. However, there is nothing that indicates that a battery protects a circuit, nor has any inherent limit on discharge, so the case of overloading with a battery is less problematic.
The main reason for creating this kind of circuit is to have multiple power generators scattered about the map, connected by cheaper wire. There have been a number of threads and comments in the forums about this (just search for "transformer"). My concern is mainly about having consistent behavior in different situations, for new and experienced players alike. A new player probably won't understand why their circuit might be overloading; indeed, it took me a few hours in sandbox to figure out this behavior.
1. Create a circuit with one transformer providing power to multiple child consumer transformers. 2. Note the values being consumed by the consumer transformers in the energy tab of the inspector. The total should not exceed the rating of the circuit's wire. 3. Add another supplier transformer to the same circuit. 4. Note the values being consumed by the consumer transformers in the energy tab of the inspector (or just wait for an overload to occur). The total will likely exceed the rating of the circuit's wire.