The USB Power Test App first negotiates a power contract for every PDO supported by the 87W adapter, and increases the load gradually to find the threshold where over current protection (OCP) kicks in and voltage and current start to drop for safety reasons.
The USB Power Test App reports out all the PDO's supported by the 87W adapter and their OCP thresholds. OCP thresholds for the 87W adapter are set at about 6-54% above the maximum current levels for the fixed PDO's.
PDO#1 Fixed: 5V 2.4A
PDO#2 Fixed: 9V 3A
PDO#3 Fixed: 20V 4.35A
The USB Power Test App from Granite River Labs also produces an I-V curve which graphically shows the relationship between voltage and current for each PDO. We can see the voltage immediately shuts off once the current increases beyond the OCP threshold.
The USB Power Test App can also use the Granite River Labs USB Power Delivery Compliance C2 Tester integrated with the GW Instek APS-7100 programmable AC power supply to compare the charger's power output vs power input so that power efficiency can be measured and compared to regulatory limits from United States of Energy (DOE) Level VI or European Union's CoC Tier 2 requirements. We can repeat the power efficiency tests for different PDO's, current load conditions, and different AC input ranges, allowing us to get a complete picture of power efficiency ranges across all different usage scenarios.