My Original Sprog 1 is suddenly shutting down when I use the Throttle ?

Originally I thought this was motor related to a Hornby Class 50 which I was
working on for a friend (Mine has never worked on Sprog - I just assumed it was
a current draw thing), but now I'm working on a Split Chassis Bachmann A4 and
this is the same, I can't get above 1\4 power before sporg shuts down. I know
this is not a short as when this occurs, Decoder Pro also freezes -All I have to
do is turn the power light back on.

I'm using the same power supply I have used for the past 7 years (Gosh have I
has it that long ?)

Anyone have any thoughts ?

Andy