Why should you need a power supply for preamp?

If you already have a power conditioner or regenerator? I mean it sounds like redundancy. For the cost of one of those preamp power supplies you could get a full system power conditioner or regenerator. I have a PS 1000 regenerator. I just bought a Bryston BP 25 with the smaller power supply to save money over the BP 26. Ive read there is little difference between the 25 and 26 anyway. Is my reasoning sound? No pun intended. Thanks all