Charging specifications have become genuinely confusing, and confusion at the shelf costs sales. A customer who cannot tell which adapter is right for their phone usually buys the cheapest one, which is the worst outcome for both of you. Here is the working knowledge a retail associate needs.
Wattage is the headline number, and it is not the whole story
Wattage describes the maximum power an adapter can deliver. A 20W adapter can fast charge most current phones. A 30W to 45W adapter covers phones and tablets comfortably. A 65W adapter handles most laptops. A 100W adapter handles almost anything.
What wattage does not tell you is whether the adapter can negotiate the right voltage with the device. That is what power delivery does, and an adapter without it will charge slowly no matter what number is printed on the box.
Power delivery is a negotiation, not a setting
USB power delivery is a conversation between the adapter, the cable and the device. They agree on a voltage and current that all three can support, then the adapter supplies it. If any of the three does not support the standard, the whole chain falls back to slow charging.
This is why a customer who buys a fast adapter and keeps an old cable often reports that nothing improved. The cable is the weak link, and selling the adapter without the cable creates a disappointed customer and a likely return.
PPS matters for some phones and not for others
Programmable power supply is an extension of power delivery that lets the adapter adjust voltage in very fine steps rather than in fixed jumps. Several Android manufacturers use it to reach their headline charging speeds, so a customer with one of those phones needs a PPS capable adapter to see the advertised result.
You do not need to teach customers the term. You only need to know which adapters on your shelf support it, so that the right one goes home with the right phone.
Gallium nitride is about size, not speed
Gallium nitride is a semiconductor material that runs cooler and more efficiently than traditional silicon. In practical terms it means an adapter of the same wattage can be dramatically smaller and lighter.
That is a genuine benefit worth paying for, particularly for travelers and for anyone charging several devices from one outlet. It is not faster than a conventional adapter of the same rating, and telling a customer otherwise sets up a complaint.
The takeaway
Wattage sets the ceiling, power delivery unlocks it, the cable can quietly cancel it and gallium nitride only makes it smaller. Put outcomes on the shelf tag instead of specifications and your average charger sale climbs.