Lets say i want to reach a certain wattage of 2,500 W. But I run it off a power source which maxes out at 5 A and 20 V. But I step the voltage up to 500 using a coil or transformer and now 5A × 500V is 2,500 but thats a lot of power from a small power source. Is stepping the voltage up really going to allow me to get 2,500 W of power from 5 A and 20 V or am I calculating this wrong? I'm new to electrical engineering and it seem strang that I can have such a power increase just by increasing voltage/amps.
Your 20 V, 5 A supply is capable of 100 Watts of power (V x I). You cannot get more power from the supply, whatever you do.
You can, however, convert the voltage. In the case of AC, you use a transformer. In the case of DC, there are many different conversion methods.
But, the maximum output power must always be 100 W! So, if you convert to 10 V, you can only get 10 A. If you convert to 1 V, then you can have 100 A. But the power won't increase. V x I can't exceed the original 100 W.
In the real world, each conversion will also have some inefficiency. So you'll actually end up with less power than you started with.
am i calculating this wrong?
Yep! By stepping up the voltage with a transformer you will still only get the same amount of power out. There's no free lunch. In this case, the current you can draw will be less, by the same ratio.