UPS with no RF noise?

[VK5TM]

Actually looking at the graphic on the unit, how did you wire it up - the generator to the two pin end and the extension cord with earth to the other end?

Yes, commonly the "two pin end" is connected to the incoming supply, the UPS in your case and the other end to the load.

That middle pin on the load side is connected to the common earth line running from the supply side to load side.