VA is an electrical engineering term deriving from the fact that current and voltage aren't in phase with each other for most electrical loads (hence PSUs having "power factor correction" to fix this).
The VA value is the (Peak Voltage) x (Peak Current), while the wattage is the Peak (Voltage x Current). Hence for a pure resistive load (no capacitance or inductance) 30VA = 30W. This will actually produce more like 25W for most real loads.
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