Weiss Elektrotechnik NGE300 Compact PSU transformer 1 x 230 V 1 x 0 V, 6 V AC, 15 V AC, 18 V AC, 21 V AC, 24 V AC, 27 V AC, 30 V AC 300 VA, 240 W 10 A

By simply plugging in into different outputs these experimenting transformers can provide 8 different voltages in steps of 3 V, AC or DC. Can optionally be fitted with an electrolytic capacitor.