The Vin powers the microcontroller, couple of ICs and an LCD. The CAP+ (just named so, i should have named it different when posting the schematic to avoid this misconception) are screw terminals connecting to a 12V LiPo. The LiPo is connected when the Vin connectors are physically disconnected. Basically the LiPo will power the board if/when the Vin is disconnected or powered down even with the connector plugged in. The DIODE in series with CAP+ prevents the Vin from merging with the 8V rail in case the Vin is powered.
Second situation where both CAP+ and Vin is powered, the PSU powering the Vin also powers a buck-converter converting the +12V from the PSU to +8V for charging the supercapacitors. The Vout terminals from the Buck-converter is connected to CAP+ (the same terminal where the LiPo would be connected) which connects to the capacitor bank. Here the Vcc pin would be powered (not sure if by Vin or CAP+). The diode in series with Vin has not role here on the other hand the Diode in series with CAP+ prevents the +12V from getting to the supercaps.
