Funding comes from two possible places the University/department or external funding agencies via grants. Who funds what depends on what's being funded, how much funding is needed, and who the money is benefiting. For (large) equipment purchases it can also be the case that external grants require the University to pay part of the cost while the external grant covers the rest. It may also be the case that there is no existing funding now, but funding can be applied for to support your research needs.
However, as a PhD student, none of this is your concern. You just need to ask your supervisor. If they think you need the equipment, they will then work out in consultation with the department where the money is going to come from.