[quickthrowman]

The vast majority of US homes use NM cable (romex) which is rated for 600v.

NEC 2020 edition, Article 334 Non-Metallic Sheathed Cable

334.104 Conductors.

The 600-volt insulated power conductors shall be sizes 14 AWG through 2 AWG copper conductors or sizes 12 AWG through 2 AWG aluminum or copper-clad aluminum conductors.

[ethbr0]

So the in-wall would be good, but the standard socket (NEMA 5-15) definitely isn't rated for 240v and would need upgrading.

[quickthrowman]

Correct, a residential NEMA 5-15 receptacle is only rated for 125v. There are some dual amp/dual voltage (15a/20a, 125v/250v) receptacles out there, but you almost certainly won’t see them in a house. NEMA 6-20 is rated for 20a at 250v.

More dual amp/dual volt wiring devices: https://www.plugsocketmuseum.nl/NorthAm1combi.html