Powell netted eight goals in 23 appearances for Wellington last season, including four strikes in a memorable 5-2 win over grand finalists Western Sydney Wanderers.
The former Sydney FC fringe player scored for the Mariners as a "trialist” in a thumping 9-0 win over a Central Coast select on Tuesday night and the club are expected to officially announce his capture on Thursday morning.
Irishman Roy O’Donovan, who Powell is expected to link up with next season in what promises be a damaging partnership, scored five in the same game.
Powell has inked a two-year deal in Gosford, having negotiated his exit from the Phoenix with a year to go on his deal so he could be nearer to family in Sydney.
The signing of the 25 year-old is a sign of intent from owner Mike Charlesworth and coach Tony Walmsley as last season's wooden spooners ramp up their recent rebuilding program, having already netted the former Sydney FC midfield duo of Mickael Tavares and Jacques Faty and Melbourne Victory flier Connor Pain.