EmonTX Shield in USA

[miq]

Agreed Robert, actually I don’t know what that 40w-50w really is, that’s just an assumption.

EDIT:
Just saw @glyn.hudson posting this minutes ago:

emonTx V3 USA apparent power

I have just noticed a bug where USA apparent power mode (when no AC-AC adapter is present), would return incorrect readings if used in the USA on 110V with USA mode enabled. This has just been fixed with firmware V2.7.0. The emonTx was incorrectly still using 240V as Vrms when USA mode was enabled. This bug is not an issue if using an AC-AC voltage sensor adapter to enable more accurate Real Power readings. Use of AC-AC adapter is highly recomenended.

Maybe the problem that the OP face now related to this?