Wow! Hate to break it to you, but tesla doesn't support J1772, except through a converter. Ask then what their maximum J1772 amperage is. If your Prius could accept that 75A, it would fully charge in under 15 minutes.
It comes with an 80AMP capable J-1772 to Tesla adapter. Here is a thread on the adapter, complete with pictures: J1772 Adapter for Model S The ITT J-1772 cable is U.L. Listed to 75A, I'm willing to give up the 5Amps to save nearly $600 (Tesla HPWC is $1,200)
My PIP sits outside with the wife's Camaro Convertible in the garage. So I initially wired an outlet near the garage door, so that the EVSE could reach the charge port. Notice the Kill A Watt. I also use one at the office. Then I added the lock, but I don't always use it. Recently I finished installing a Yard Lamp Post, so that I can charge while parked next to the driveway. Here is where the power comes from for the lamp post. Finally, at work, instead of using an extension cord out the basement office window, I installed an outlet on plexiglass with its Kill A Watt inside. The building owner wouldn't let me install an outlet on the block wall. Those are my setups, at the house and at the office.
What kind of extension cord are you using? Looks like the wrong gauge, but hard to tell from this pic. That said, great & clever setup!
The 1st photo with the outlet near the garage door has an Appliance cord, 15 amp rating. I used it for its right-angle plug, instead of plugging the EVSE directly into the Kill A Watt and getting pulled out with the cord weight.