As Rolls Royce would say, "adequate".
But I assume you're wondering in the context of 31 bhp claimed for the Vertigo. I imagine if the Ossa differed significantly from the low twenties quoted for a Gas Gas the last time I saw a published figure for a modern bike then they'd have shouted about it.
For what it's worth, the original Sherpa claimed 18 bhp if I remember correctly. There's a good reason why bhp figures have not (until Vertigo) risen much and it's to do with rideability, though with World sections now bhp may be more important than the old days when it was torque that counted more in a trials bike.
I can't recall a posting asking how to increase the power of a bike but there have been plenty along the lines of "how can I detune my XYZ?". Which makes one wonder how much of a sales point a comparatively large bhp for a new bike will be in the mass market.
