Here's someone's pic with a cord plugged in. This was also sold for the Japanese market Prius PHV.
And a full explanation from Toyota, albeit in Japanese:
Translated by Google:
How to use Prius PHV Vehicle Power Connector
* Please check the following 4 points before supplying power.
・ The parking brake is applied.
・ The headlamp is off.
・ The power switch is off and the engine is running. It is in a state where it does not cover.
・ The bonnet is closed.
1 Press the power switch twice without stepping on the brake to turn on the ignition. (Ignition ON (right) is displayed on the display
Please make sure it is done)
The advice screen for starting operation (lower right figure) is displayed.
If this happens, press the meter operation switch (see page 2) attached to the handle to return to the previous screen. If you do not operate the meter operation switch for a certain period of time, the advice screen for starting operation will be displayed again.
2 Use the meter operation switch (shown on the right) attached to the handle to switch the display.
Press (right figure) to switch the display contents (setting screen).
By pressing (right figure), change the item for which you want to change the setting, select (Vehicle customization), and press the OK button (right figure).
3 Use to select and press External Power Supply in the Vehicle Customization menu (figure on the right).
Meter operation switch
Then press to select the power supply mode and press. The figure on the right is the EV power supply mode screen. The difference between EV power supply mode and HV power supply mode will be explained on the next page.
4 When the confirmation screen appears on the display, press “OK”. (Lower left figure). Then use to select the vehicle power connector and press. (Lower right figure).
* Power supply mode
■ EV power supply mode External power supply is performed using only the power stored in the drive battery. Power supply will be terminated when the remaining amount of drive battery that can supply power is exceeded.
■ HV power supply mode If the remaining amount of the drive battery that can be supplied with power is reduced while the external power is being supplied, the engine will start.
It operates and continues power supply. When the fuel level warning light comes on, power supply ends.
Since the engine operates, it is necessary to park in a well-ventilated place.
5 Plug the electrical outlet into the outlet of the vehicle power connector.
6 Insert the vehicle power connector into the normal charging inlet (below) of the PHV charging port.
7 If you press the power switch on the upper side of the vehicle power connector twice in a row, the charge indicator will change from blinking to lit after a while. After turning on, turn on the power of the electric appliances.
Can supply power up to a maximum power consumption of 1,500 W or less
Subaru of America, are you listening, this is what we want on the Solterra, although obviously with a 5-15R connector.