Which ink does the Epson Expression Home XP-420 use?

The Epson Expression Home XP-420 uses Epson 220 and Epson 220XL.

No. The Epson Expression Home XP-420 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 Home XP-420 toner, the part you want is Epson 220 and Epson 220XL.

Yes. Besides the standard cartridges it accepts Epson 220XL. 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 Home XP-420 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 165 pages (Epson 220) to about 500 pages (Epson 220XL), 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 220XL at about 4.4 cents per page. A reliable compatible or remanufactured cartridge can lower that further.