Question about power supply for the O2 headphone amplifier

So I recently purchased an O2 headphone amplifier that comes with a WAU12-200 power supply.

Some quotes from NwAvGuy’s blog:

In North America the Triad WAU12-200 from Mouser is rated at 12 volts but is really about 13.5 VAC with no load, and on normal 120 volt line voltage works fine for anything but full power sine wave testing or driving rare low impedance power hungry cans. If your line voltage is below 117 VAC or 235 VAC, and/or you plan to drive difficult low impedance headpones (i.e. HiFiMan planars), I would suggest a 14+ VAC transformer at 400+ mA.

In real world use, the WAU12-200 is the least expensive option and works fine at normal line voltages playing music (not sine waves) into 99% of headphones.

The power supply, with a 13.5 VAC (no load) wall transformer, is right on the edge of letting some ripple though under worst case conditions. If the O2 is used with low line
voltage, and for sine wave testing, or using very power hungry low impedance headphones, a higher voltage transformer is recommended (14 – 20 VAC).

Now I have more powerful amps, but I just wanna make my O2 compatible with all my headphones. The only planars I have are the HE-400 , T50RP MK3 and I have plans to buy either the Deva pro or the Sundara. Should I buy a 14V AC+ adapter or is my adapter good enough for the headphones that I have / plan to buy ?