The device on a shelf may earn its retailer very little. The cable, case or adapter sold with it frequently earns several times more, and the pricing follows directly from when each is bought.
Hardware competition compresses the main margin
Popular devices are comparable across retailers, easy to search by model number and heavily advertised, so their prices converge tightly.
Selling them is close to a commodity business, with margins measured in low single-digit percentages once costs are counted.
Retailers accept that because the device brings the customer. The profit is expected from what happens next rather than from the box itself.
Accessories are bought without comparison
An accessory is usually chosen in the same minute as the device, when the shopper has already decided to spend and wants the purchase complete.
At that moment the effort of comparing a cable across three sellers is out of proportion to the sum involved, so almost nobody does it.
Prices can therefore sit far above the online level for functionally identical items, and the difference survives because it is never tested.
Proprietary connectors narrow the field
Where a device uses a connector or fitting unique to its manufacturer, third-party alternatives are limited and sometimes licensed.
Licensing programmes add a per-unit fee and a certification requirement, both of which raise the floor price for every compliant accessory.
Standardised connections have the opposite effect, which is why common cable types have collapsed in price while proprietary equivalents have not.
Store layout and prompts do the work
Accessories sit beside the devices they fit, at the till and in the checkout flow online, because proximity to the decision is what makes the sale.
Online recommendations perform the same function, presented as helpfulness rather than as the highest-margin item that fits the product just added.
Extended protection plans belong to the same category. They are sold at the same moment and for the same reason, with cost bearing little relation to price.
Separating the two purchases restores the comparison
Nothing requires the accessory to be bought with the device. Buying it a day later, from wherever is cheapest, returns the decision to a normal comparison.
For cables and adapters the saving on a single item can approach the accessory's full in-store price, and the specifications are usually published clearly enough to match.
The one case for buying together is where compatibility is genuinely uncertain, since returning a mismatched accessory costs more than the difference saved.