Flarm is GPS based; all pylons, masts and aerial cables are in its database. Anybody can add new obstacles by sending their coordinates to the developers.
You can achieve a more general GPWS function with a Garmin 496, which contains a terrain database produced by the space shuttle radar, supplemented by an obstacle database, and which is accurate to around 200ft for Europe. You get TERRAIN TERRAIN PULL UP type verbal warnings (which can be linked to the aircraft intercom) plus a little map pops up showing which way the obstacle lies so you can turn to avoid it.
I have one of these on my yoke; it has been tested pretty well against various terrain in Wales and elsewhere and short of actually flying into a few hills I reckon it does what it says on the tin. AFAICT the database is identical to the certified version used on the GNS530. And you get a pretty good aviation GPS, for ..... navigation
OTOH if one is flying at high voltage pylon level, all bets are off and one can hardly call that kind of stuff "VFR flight". The professionals that do that sort of low level flying (S&R, power line inspection, etc)
AFAIK fly dual-crew and they use the 1:25k or 1:50k O/Survey charts - I have used these and similar charts and they are mightly difficult to use while flying single pilot. They also use helicopters so when the cloudbase reaches the ground they land, have a pee and unpack the sandwiches
The BGA are looking at FLARM for the UK, but at the moment it is technically illegal to use it in UK airspace
Why? An active (radiating) device might be but a passive GPS based one cannot possibly be illegal.