Those ratings don't necessary have to mean anything.
A proper 2A supply can be better than a crappy 4A one.
A good PSU keeps the voltage constant up to its rating and then shuts off due to over-current protection.
The voltage of a poor PSU will start to break down under load, often long before its max current rating is reached. The result is having weird issues with your board.
At customer grade sector its a matter of luck to get something proper. The only way to be certain, if you cannot do measurements by yourself to verify, is picking up something industrial grade.
Also most SBCs like being fed with slight overvoltage. About ~5.2 volts at the source. Last but not least to compensate for losses across wiring and connectors.
Some PSUs already do that. Even when labeled 5 volts measurements usually show something between 5.1 and 5.4 volts. Depending on quality like described above this breaks down under load or is kept constant.