How PoE works
A PoE switch injects power into the Ethernet cable, alongside the data, and the powered device draws that power from the cable, so one cable serves both purposes. The switch's power budget is the total power it can deliver across all its ports, and a buyer must ensure the budget covers all the devices at once, not just one at a time, because a budget that covers each device singly but not all together will fail when all devices draw power at once.
Choosing by budget and ports
Add the power draw of every device, add a margin for growth, and choose a switch whose budget covers the total, because a switch cannot deliver more power than its budget allows. Count the devices, add the uplinks, add a spare port, and choose a switch that covers the total, because a switch cannot gain ports after installation. Confirm the budget, the port count, and the rate for the exact devices, in the inquiry, before ordering.
What to confirm before ordering
Name the switch type, the devices it must serve, their power draws, the quantity, and the market. Ask for the specification for the exact model, the minimum order quantity, the lead time with its meaning, the warranty terms, the payment and shipping terms, and the certificates that apply to your market, by name, with documents attached.
Before payment, confirm the minimum order quantity, lead time, payment, shipping and warranty terms for your order. Certificates are available upon request.