Using a 5A power supply for an LED Strip rated for 3A per color
Typical LED strips have fixed current usage, due to the 3 diode + 1 led setup. A PSU with a higher current capacity will not change this. It would only allow you to power a greater length of led strip.

If you have issues with brightness at the end of a long run of a led strip, this is due to the high resistance of the copper FPC used. The main way of getting around this, is to feed the power at both ends, at the middle, or every few meters.

Attempting to power a given length of LED strip with a supply that cannot provide that capacity, will result in a burned out PSU.

Edit: Of course, your strip is the 150 RGB leds per 5 Meters. That's 50 3-Led segments, 0.02A per segment, or 1 Amp per 5 meters, per color. Your strip only needs a 3 Amp supply. The typical 2 Amp per color strips have 300 leds per 5 meters, twice of what you have. Led strips come in all sorts of configurations, and the number of leds per meter is one of them, as well as led type/size.