A (very) quick Google suggests a currently-available drop-in replacement for airliners is the
VHF-2100 from Collins Googling
that shows a minimum of 25w output power in
this document (though it seems to be more VDL than comms oriented).
This FCC Document shows the VHF-900 (replaceable by the VHF-2100) also has a 25W carrier so that might be the common standard.
With VHF, if I remember my basic RT, you don't need a massively powerful transmitter as it's line-of-sight limited, a relatively weak transmitter still has quite a long range in the atmosphere, though happy to be corrected, been many a year...
Hope that helps.