We generally just use bog standard entension cables too. Haven't had any problems for years.
If you are having problems with noise and interference from your power source, then I'd do what Ailean suggests and just stick the short hi-fi power conditioner in the end of a long standard extension lead.
Only once do I remember playing anywhere with real noise problems from the power, and that was at a scout hut in the middle of nowhere, with an enormous, power hungry, stage lighting rig. I'm fairly sure the lighting was the main problem as it was all running from the same extensions as the amps/PA etc
