There are physical limits to the size, mainly determined by the size of the filter capacitors in the front-end power supply. The capacitors have to have enough microfarads to supply current between AC cycles. There also has to be a transformer and those can be made smaller, to a point, but there are limits there too. The reason I say reasonably sure without damaging the monitor is that the internal regulators that operate off the 12vdc, normally will now get hotter because of the higher input voltage. This could eventually cause a failure of the internal regulator if it gets much hotter than the design can handle. But this should be OK if the monitor is not used in a room that is excessively hot like 40–60°C. My laptop is rated "19.5V - 3.34A / 4.62A", should I buy a 65W or a 90W AC adapter?

The adapter output voltage needs to closely match the monitor requirement. (V-monitor -1v)

Excessive voltage can damage your device, but excessive amperage won’t (the device will only draw as many amps as it needs) Adapter has 13.5vdc output. Monitor requires 12vdc. 13.5vdc > 12vdc OK. 13.5vdc < 12vdc + 2vdc = 14vdc OK. PCG-61315L PCG-61317L PCG-61511L PCG-61611L PCG-71311L PCG-71312L PCG-71313L PCG-71318L PCG-71811L PCG-71913L Sony Vaio PCGA-A Series: All Models, Sony Vaio VGP-A Series:VGP-AC19V2 VGP-AC19V10 VGP-AC19V11 VGP-AC19V12 VGP-AC19V13 VGP-AC19V19 VGP-AC19V20 VGP-AC19V21VGN-CR309E/R VGN-FS620/W VGN-N250E/W VGN-NR180E VGN-NW240F/S VGN-NW310F VGN-AR VPCEE25FX SDM-M51 SDM-M51D SVE11125CXB SVE11125CXW SVE111B11L SVE15135CXW SVF142C29L SVE141L11L KDL-48W590B KDL-48W580B KDL-48W600B KDL-40W600 First the power requirement of the monitor must be known. This information is on the product safety label usually on the rear of the device. What is needed is the voltage and current or voltage and power requirement. PCG-91311L PCG-4121Gl PCG-61A14L PCG-61411L PCG-71911L PCG-71912L PCG-3G2 PCG-5N4L PCG-5S1L PCG-5S2L