In a common atx PSU has several voltage outputs with different amperage capacities such as 3.3V 25A, 5V 28A, +12 15A, - 12 1A. My question is simply that, if I make a connection positive side from +12V with 15A capacity and negative side from - 12V 1A capacity, then I will have 24V but what about the amperage? It will be 7-8A as total power of positive side or limited to 1A because of -12V capacity?
If you need to power something with 24V then you'll connect the -12V to the negative terminal and +12V to the positive terminal. The current that can flow in such a configuration is as much as the -12V terminal can source, meaning 1A.