Yes, it's sufficient for your router but only one S7. It will get pretty warm but not hot with one router and one S7 on that 16 AWG extension cord. I'm assuming your are using a PSU(s) that can also plug into 120V?
Okay. I think I will be headed out and grabbing a 12 AWG rated extension cord or better. 'pretty warm' disturbs me. I don't intend to run the router off of it. It's fine where it is. I'm just not able to feed power to the S7 from the same bedroom where the router is. The S1s weren't a problem because they were wireless. But since the S7 is a direct-line into the router, I sort of need to keep it close to the router with a long extension cord, or a bit further away from the router with a long CAT5 ethernet cable.
14 AWG extension cord would certainly be fine but 12 AWG even better. However, 12AWG can be expensive compared to 14 AWG. 14 AWG is certainly much better than the 16 AWG on that 15 amp outlet.