Agreeing with others, for the most part: assuming it is, in fact, a fuse on the main line from the wall outlet to the transformer, it's essentially impossible that 5 amps (or 3, for that matter) is too low.
Five amps at 240 volts = 1200 watts. No effects box requires anything close to 1200 watts from the wall. If they did, each one would need to be on its own circuit (in the US) to avoid blowing the main fuses.
Yes, an effects box might draw 1 amp from its transformer at 12 volts (or so). That's 12 watts, which is a far cry from 1200. True, the transformer in a wall wart is pretty inefficient, but if it were losing 1188 watts you'd burn yourself if you touched it, and it would probably set the carpet on fire. That's more than a normal hair dryer, and about the power of a small stove burner. Using a figure at the high end of what's possible, a very inefficient transformer might lose as much as 80% of the power it draws: to get 12 watts, it'd need 60, which means it would draw 1/4 of an amp. If a 5 (or 3) amp fuse blows at 1/4 of an amp over any period of time, there's something wrong with it.