OK I have now found a fix …
Forget all that concern over regulated (non) power supplies, wall warts or power conditioning for generators or concerns over voltage drops. I have just purchased one of these:
It's a 12Ah batterry power pack designed for charging mobile devices. It has 3 selectable voltage outputs 5v, 9v, 12v so running at 9v it will keep my single Pitchfactor going for 24 Hours. It can supply up to 2Amp so should run up to four of these power hungry stomp boxes for about 6 hours in theory. I used it last night – all good and the power meter didn't drop a single level over 3 hours.
Best of all it cost just over £40 and can be used to recharge your phone/ipad….etc if needed. feels pretty sturdy although I hide it under my monitor.
What's not to like?