We just got our new UPS in and it has a 120v 20Amp NEMA 5-20P plug on it. Our outlets are 120V 15Amp NEMA 5-15P. My question is: Is an adapter plug a bad idea? Or should I have an electrician come ...

Voltage? I'm going to guess you are getting 2 20Amp 120V circuits, if the plug is a NEMA 5-20R you can do a 20Amp PDU if its only a 5-15R you can only do a 15Amp unless you get creative with ...