Which power supply topology is this?
This is indeed a variation on SEPIC.  Remember in SEPIC, although "technically" there are two separate inductors, in practice often they're combined onto the same form (and are thus coupled directly) to reduce costs and bulk.  Since both inductors carry similar voltages, with proper phasing they can share the same core.

The difference here is that the "switch" T1 sinks its conduction current to the output rather than ground.  This implies to me that the output is quite a bit lower in voltage than the input -- really a combination SEPIC with a buck twist.  If you separate N1 and N2 (write them as separate inductors, ignoring the common core) the topology is identical with Figure 1 in the wikipedia article except that T1 connects to the output instead of ground.  Incidentally this adds a 2nd source of output to the circuit -- not only the diode output, but also the source of T1.  So the designer introduced "current sharing" resistors R1 and R2 which connect both "incoming" sources to their common output.

I bet R1 and R2 are identical (or nearly so).  That would further confirm that the voltages across the inductors are similar and that their common core is not functioning like a transformer so much as it is a common host to two inductors whose interfering magnetic influences are, in fact, not a problem in this particular case.