The device is apparently one of the switches in a SMPS.
The base part is a 30V (Vds) rated N channel device in a TO-252 (DPAK) package.
If you cannot get one of these, then look for a device that has the following parameters close to the original (these are the primary parameters in SMPS device choices):
\$V_gs\$ (max) : keep within the range of the original part
\$Q_g\$ (total) : as low as possible, no higher than the original (but not too much lower either - this affects transient performance significantly and too low could cause interesting issues).
\$R_ds\$ (on) : as low as possible, no more than the original part.
The diode conduction parameters are also a key concern, as many cheap supplies rely on this diode rather than fit an external device for cost reasons.
Make sure you find a part with very similar \$I_d\$ parameters.
Ensure that the absolute maximum rating for any replacement are at least as good as the original part.
Many manufacturers have parametric search capabilities. Try Vishay, International Rectifier, Fairchild and Diodes Inc for starters.
I looked at the IPD050N03L from Infineon (looks like an original IR part) and the only specification that is significantly different is diode avalanche pulse energy; interestingly, the original datasheet does not even have a safe operating area graph.
The key parameters are marginally better (and the gate charge and input capacitance are similar, so switch turn on and turn off time should be the same as the original).
Overall, it looks like it should do the job.
Based on the latest comment, I suggest using the parametric tables to find a device with headline parameters of:
\$I_D\$ 50A or higher
\$Q_g\$ around 10 to 20 nC
With a filter on the package of DPAK (TO252)
Then look at the other parameters. Something with these specifications should do the job.