Certainly not. Maybe the PC power supply will also fail to give such currents on -5V line. The -5V exists in the PC power supplies as a backward compatibility, some time ago, memories, especially old ones required -5V to operate, but in modern PC boards, this voltage is not used. This is why the manufacturers do not put a high price on the -5V line, it just have to be there, that's all. But it worth to check the label from the power supply, the current capabilities are usually indicated.
/pisoiu