Which ink does the Epson Expression Premium XP-820 use?

The Epson Expression Premium XP-820 uses Epson 273 and Epson 273XL.

No. The Epson Expression Premium XP-820 is an inkjet, so it prints with liquid ink from a cartridge, not toner powder, and no toner cartridge fits it. If you were searching for Expression Premium XP-820 toner, the part you want is Epson 273 and Epson 273XL.

Yes. Besides the standard cartridges it accepts Epson 273XL. A high-yield XL holds more ink and costs less per page, which is worth it if you print often.

Epson can stop third-party ink working here with a firmware update, and it is the update rather than the cartridge that does it. This one is weaker than the rest of the list and we would rather say so. The guide Epson published for the Expression Premium XP-820 carries no ink note, but it was written before Epson began printing one, and Epson's current position covers every cartridge printer it sells. Hold firmware updates if compatibles matter to you, and treat a cartridge that stops being recognised right after an update as the expected failure rather than a faulty cartridge.

Rated yields run from about 250 pages (Epson 273) to about 650 pages (Epson 273XL), depending on the cartridge. Real-world yield depends on how much you print and how much ink each page uses.

By list price the lowest cost per page here is the Epson 273XL at about 3.4 cents per page. A reliable compatible or remanufactured cartridge can lower that further.