What do you recommend in terms of power supplies for hi-fi gear in older premises?

Power can be a real issue in older houses, so here are a few suggestions.

The first might seem obvious, but have everything checked and tested by a qualified electrician. This can identify and rectify wiring and ground issues, broken outlets etc. Power outlet testers like this one allow end-users to identify miswired outlets, ground problems and so on and are a good starting point.

Next, assuming you have safe, correctly wired outlets, you need quality power distribution. Multiple wall outlets are best, so ask an electrician or your landlord if this is a possibility. Failing that, I suggest the best powerboard you can afford. One bigger one is better than daisy-chaining them, which should be avoided.

Amplifiers and other high current equipment should ideally be plugged into the wall directly, rather than through a power board, where possible. Older gear may have grounds/earths lifted or removed, so this must also be carefully checked for safety and performance reasons.

Mains filters are useful in some cases and can be purchased from hi-fi stores. These may reduce noise and improve system performance. Regenerators offer the best performance but are also very expensive and usually not suited to high current devices.