The schematic is fairly simple and i really wanted to avoid to use a MCU to make it easy if i decided to make some kind of product of it.

Ill try to go thru the block of the schematic and try to explain on how it works.. in i higher level.

"Input block"

The input block is really simple and is basically made up by Q1 which is used for reverse polarity protection and a LDO with 5V output to power the internal circuits on the boards.

"OVP block"

A simple low cost OP connected as comparator that enables the load switch Q8 to supply the USB-A and USB-C Vbus. This is if the input voltage is below 5.6-5.7V. When above there will be no output voltage to protect the DUT.

The switch S1 will ground the input of the comparator and forcing the output  to enable the load switch. This disables the OVP and pass thru voltage.

Vbus for USB-C is not on by default and is controlled by U2. Therefore to also force Vbus high the switch also controls Q2 regardless what is negotiated on Vbus C. 

When OVP is disabled the orange LED D8 is turned ON to notify user that OVP is not active!

"USB-A negotiation"

Vbus for USB-A is always enabled according to the standard and the U4 IC basically tells the DUT that the maximum allowed charging current is 2A (10W)

"USB-C negotiation"

By default the Vbus for USB-C is disabled and is only enabled when a successful negotiation is performed with the DUT. This is entirely handled by U2 which also can allow up to 3A charging current (15W).