It is an Arduino UNO, and I connected the power supply by the barrel socket on the fron of the arduino.
I've used 9v power supplies with barrel jacks to power arduino's with led strips before, and though a 5v would be ok. Apparently not tho'
The barrel connector feeds to a reverse polarity protection diode and linear regulator that results in a loss of around 2 volts, before it gets to the Arduino, and to the "5V" volt pin. In other words, the printed "5V" is hopeful but not necessarily true. It's veracity depends on adherence to specifications, such as "7 to 12V" on the Barrel connector.