What Riko is saying is that with the
standard 1.5 Powerbase there is no point in having more than the 5 Amps, which 2 x C7004 PSU will happily supply. This is because the most current that can be drawn from a standard Powerbase is 3.5 amps.
However if you have the S-H Power upgrade then up to 20 Amps continuous and 30 Amps peak can be supplied.
Even a standard 18000 RPM Scalextric car will
try to take 1.5 Amps when pulling away from a standing start, so with 6 cars that is 9 amps. Higher RPM motors will try to take even more current, with an NSR 30K Shark taking 6 Amps.
So.... this is where greater than 10 Amps comes in handy.
Of course the running currents are much lower, which is why you can
get away with much lower currents, howevr if you want that responsive analogue feel then S-H and a big PSU is the way to go.
Rich