It sounds normal (unless you are having other issues). These transformers don't usually have a very stable voltage (especially when there is no load). When you are testing, it may show 19v, but when it is actually charging, it is probably closer to 15-16v.
Internally (in the vacuum), there is probably some voltage regulation that will take whatever is coming in (whether 15v or 19v) and take it down to whatever is required to charge the batteries (say 12v or 9v). Some devices will also have circuitry to avoid overvoltage, reverse voltage, etc.. However, with the constant demand for things to sell for less and less money, some of this additional circuitry may be removed from the device (since it might add 10 cents per unit (or whatever)).
In short, everything sounds normal. I wouldn't worry about it.