Question about Cooler Master MasterBoX Q300L

Any ATX power supply fits without problems, only the motherboard you have to be careful that you have a mATX or Mini ITX.

Power supply is more a question of what power your components need and what efficiency is important to you. The case offers few cable management options and is well ventilated but not the first choice for really power-hungry components. The ATX power supplies needed for a budget build should all fit without any problems.