I’ve seen a LOT of threads asking the same question, so stikying this would be useful.

If you’re going to change your power supply (ps) then you must look into this:

input voltage: if your country runs on 220, then the ps must have 220v on the input, if it’s 110, 110 and so on
output voltage: it must be exactly what the pedal needs. Not more, not less. More can and maybe will burn the pedal, and less will make it work unproperly (but it IS safe to undervolt/sag a pedal)
output amperage: it must be at least what the pedal needs. More is fine, less isn’t. So, if you have a pedal that runs with 45mA, the ps must supply 45mA or more.
Polarity: If the pedal needs center negative/tip negative/negative ground, etc. then the supply must provide the correct polarity.
Type of conector: must be same size, if not, won’t fit, and cause problems
Type of current: If the pedal needs DC (direct current) the ps must be an AC/DC one. If the pedal needs AC (alternating current) then the ps must say AC/AC.

If you have a power strip or a pp2+ or onespot, all of this applies also.

Extra tip: It’s better if the power supply is regulated and filtered. Because unregulated supplies provide more voltage than it says, and then, when the pedal takes the current, it gives the right voltage, which can make it not work 100% fine.

If you need to power up several pedals (more than 1) then use a 1spot (daisychain) a pp2+ (isolated grounds) and there are many others within a wide range of prices.

about daisy chaining:

Positive ground: Some pedals, such as the Nano Clone and Nano Muff OD have positive ground, instead of negative ground. They are normal polarity though. When daisy chained with pedals that are negative ground, they will not work properly. Pedals with positive ground must be on a separate power supply, or on a separate output of a power supply that has isolated outs.

Digital and analog pedals usually don’t daisy-chain well together. Digital pedals should either have their own power supply, or their own output on a power supply that has isolated outs.

Thanks to Julian and Ron