WHATEVER is the internal power supply inside all 29 pedals.
It accepts 7.5 to 35 volts of AC or DC in either polarity. That basically means that anything with the standard 2.1mm DC jack will work. If you have a supply laying around, it will work.
Internally, the voltage is triple-regulated to apply proper +/-15 volts to the audio circuit. This means 30 volts of swing, which is coincidentally higher than 9 volts and 18 volts. This means all 29 Pedals are running internally at about three times the conventional 9 volts applied to pedals.
With conventional pedals, in some cases it can be beneficial to apply higher voltage - to increase headroom, or change the tonal response in some other way. That's not necessary with WHATEVER. The extra voltage is just dumped.
The WHATEVER supply will briefly peak at 150mA on startup, so make sure your supply has at least 150mA available. Many older power bricks only supply 100mA or less per slot, or share the total current between pedals. If there is not enough current being delivered, you'll see the LED pulse. Sometimes the pedal will still function normally, but you should correct the issue as soon as possible.
WHATEVER is self-isolating, but we still recommend using an isolated supply whenever possible. Just to be extra sure. Ground loops in pedal boards can cause a lot of noise.