Hi Al.. and Thanks for the reply...
interesting answers coming my way.. what a great radio it is, but i
read 'all' the postings on this NG last night,
and it was interesting.

The supply cable is in very good condition, far as i can tell, but i
will peel back the black PVC bit on the radio end tonight,
and also check inside. the crappy CB quality fuse holders were hot
last time i attempted 100w FM,
they were glowing once on my old FT 890 AT radio - the PSU seemed to
cope with that set.
there are 3 or 4 clip-on ferrite's on the 870's DC cable already - which
is nice.

i don't have a ground here, i am on the 3rd storey, so a non-inductive
ground would be pretty tricky to organize.
and 99% of my QSO's are local rag chews on 10m anyway. but i will bond
to the cold water system this evening, but i know that may be next to
useless here.
The voltage drop at the PSU terminals is, of course 0.2 of a volt or so,
not really worth mentioning - but if i take the lid off the 870
later i guess i should be able to check for any drop inside the TRX. i
may also just 'build up' around the fuse holders with solder too,
this may help. seems the PSU lead is clean, the guy i bought the 870 off
of was using a PSU too. its a 2001/2002 serial 870 too.
i did fit another 4ft of red/black 25A DC cable via HD connectors
earlier this year, but didn't keep them on long, though it seemed ok.
i guess i need to test the cable under load.
last night on 10m FM i got the PSU supplying 15A - 16A which i guess is
on for 10m, but depending on the ATU / load it usually
draws approx 10A no matter what. strange. 14A - 70w ish on a dummy load
seems a little low, i guess i should use a amp..
but on 10m i will keep doing tests, my next test may be to take the
set to a friends QTH and use his PSU / ant..

Thanks Al. and Gwatts -
i shall do more digging
Mark