US law (and therefore US Sailing prescriptions to the racing rules) require you to have USCG certified Type I, II, or III personal flotation devices (in good condition, of appropriate sizes, accessible) for each person aboard. Children under 13 must wear a USCG approved pfd when underway (with some exceptions). Boats 16 feet and over must also carry a type IV (throwable) PFD. Additional laws apply and state laws may add other requirements.

Technically, the law and the rules don't say that the PFD an adult wears must be USCG certified. Therefore you could wear a CE or ISO certified flotation device provided you also had a USCG certified PFD aboard (in good condition, of appropriate size, and accessible). Watch out, however, for regatta NORs and SIs that may change rule 40 and require you to wear a USCG PFD.

See http://www.ussailing.org/race-officials/rules/personal-floatation-devices-pfds/ for more information.

I hope that helps,
Eric