labtop charging

Not sure why you'd assume that 4V less than specified would be a good choice.

Perhaps it would work (if the item is designed with lots of slop on the power input side), probably not. Most adapters run at or above the specified voltage. The usual problem with most "battery eliminator" type products is that they can't even get close to the required current for a laptop. Some can, most cannot.

I just use a common bench power supply set to the specified voltage when doing this type of thing - or another laptop adapter which has similar voltage and similar or greater current, with plugs hacked to match.

Try these: they cost $8USD - $12USD

if none of these fit they also have "universal" models for about $20USD. The price includes postage and there is no minimum order size. I use them (both the company and laptop power supplies) they are good.

steve Inscribed thus:

Its worth noting that some manufacturers put a one wire interface into the PSU/Charger making it difficult to use anything other than an original PSU.