Seems to me that if you use a plug-in power supply to replace a battery you need to think about isolation. Some may be safe and some not. Do these testers have a line connected chassis?

amuller, here are the specs, I am not an electrician by any stretch of the matter: Tell me what you think…

Thanks

Richard

Type of power supply unit: switched-mode
Output voltage: 7.5V DC
Maximum output current: 5.34A
Kind of output connector: 5,5/2,1
Power: 40W
Supply voltage: 90…264V AC
Supply voltage: 127…370V DC
Body dimensions: 125 x 50 x 31.5mm
Kind of case: desktop
Kind of power supply: volatage source
Operating temperature: -30…60°C
Kit contents: without power cable
Protection: anti-overload
Protection: anti-overvoltage
Protection: short circuit protection
Length of output cable: 1m
Conform to the norm: Energy efficiency Level V
Connector variant: straight
Kind of input connector: IEC C14
Efficiency: 85.5%
Polarisation: positive inner pin
Manufacturer: MEAN WELL